How to Make Perfect Oatmeal Whoopie Pies with Marshmallow Filling

If you enjoy oatmeal cookies, you’ll love these oatmeal whoopie pies. They are soft with just the right chew, and the marshmallow buttercream filling adds a creamy, gooey touch. They’re also great for sharing (or keeping for yourself!) and will surely be a hit at parties, bake sales, or any day that needs extra sweetness. These cookies are the kind of treat that brings back memories of afternoons baking in grandma’s kitchen, and they’re just as tasty the next day (if they make it that long!). The best part? Making them is as enjoyable as eating them!

close up view of oatmeal whoopie pies.

Oatmeal Whoopie Pies

Soft oatmeal cookies hold a generous amount of marshmallow buttercream. These are sweet, nostaglic, and delicious.
Prep Time 30 minutes
Cook Time 20 minutes
Total Time 50 minutes
Serving Size 12 servings

Equipment

  • Electric Mixer
  • 4 Baking sheets
  • Mixing Bowls (medium and large sizes)
  • Measuring cups and spoons
  • Rubber spatula
  • Cookie scoop or large spoon
  • cooling rack

Ingredients 

Cookies

  • 1 cup unsalted butter softened
  • 1 cup brown sugar packed
  • 1 cup granulated sugar
  • 2 eggs
  • 2 teaspoons vanilla extract
  • 2 cups all-purpose flour
  • teaspoons cinnamon
  • 1 teaspoon baking soda
  • 1 teaspoon baking powder
  • 1 teaspoon salt
  • ½ cup milk whole preferred, but 2% is okay
  • quick oats not instant
  • old-fashioned oats

Marshmallow Filling

  • 12 tablespoons unsalted butter softened
  • 1 cup powdered sugar
  • 1 teaspoon vanilla
  • ¼ teaspoon salt
  • 2 cups marshmallow cream such as Marshmallow fluff brand

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Instructions 

Make the Cookies

  • Prep.  Preheat your oven to 350°F (175°C) with oven racks in upper-middle and lower-middle positions. Then, line four baking sheets with parchment paper.
  • Combine the wet ingredients.  Beat the softened butter, brown sugar, and granulated sugar at medium speed until light and fluffy for about 5 minutes. Then, add the eggs one at a time, followed by the vanilla extract. Continue beating until well combined, scraping down the sides of the bowl as needed.
  • Combine the dry ingredients.  Whisk together the flour, cinnamon, baking soda, baking powder, and salt in a separate large bowl.
    dough for whoopie pie in mixing bowl.
  • Combine both.  With the mixer on low speed, add half of the dry ingredients to the butter mixture, then half of the milk. Repeat, ending with the dry ingredients, until all are incorporated. Mix just until combined. Add the quick and old-fashioned oats, stirring by hand or on the lowest mixer setting until evenly distributed.
  • Shape.  Scoop 3–4 tablespoons of dough per cookie onto the prepared baking sheets, spacing them about 2 inches apart. Each baking sheet should fit about six cookies; you’ll have 16–24 cookies.
  • Bake.  Bake the cookies at 350°F for 15–18 minutes, rotating the baking sheets between racks halfway through baking. The cookies should look set and slightly golden at the edges, and a toothpick should come out clean. Transfer to a cooling rack and allow them to cool completely.
    fully baked oatmeal cream pies

Make the Filling

  • Make the filling. In a clean mixing bowl, beat the softened butter and powdered sugar on medium speed until smooth and fluffy, about 3–4 minutes. Add the vanilla extract and salt, mixing until combined. Add the marshmallow cream and beat until the filling is smooth and fully combined. If the filling seems too soft, refrigerate for 10–15 minutes to firm up.
    whipped marshmallow filling.
  • Assemble the whoopie pies. Spread about ¼ cup of the marshmallow filling onto half the cookies’ flat side. Top with the remaining cookies, pressing gently to create a sandwich. Serve immediately, or refrigerate the whoopie pies for a firmer filling.
    cooling rack with cookies adding filling.

Notes

Make sure your butter, eggs, and milk are at room temperature before you start mixing.  This helps them blend well and makes your cookies have a better texture.
Check your baking powder and baking soda to make sure they’re fresh.  These ingredients lose power over time, so always look at the expiration dates.  Fresh leavening agents will help your cookies be soft and light instead of flat or hard.
Using too many oats can make the cookies dry and heavy.  Measure your oats carefully for the right amount and get that chewy texture.
Let the cookies cool completely before adding the filling.  If they’re even a little warm, the marshmallow filling will melt and slide off, making a sticky mess.
If you like a lot of filling, think about making an extra half-batch to add more to each whoopie pie without running out.
After you put the whoopie pies together, chill them in the fridge for 15–20 minutes.  This helps the filling set and makes them easier to handle, especially if you want to save some for later.
Try adding mini chocolate chips, shredded coconut, or raisins to the cookie dough for something different. Just don’t add too much so your cookies stay soft.

This recipe has everything I love about a good homemade dessert—simple ingredients, great taste, and the right sweetness. I enjoy how the soft, chewy oatmeal cookies pair with the marshmallow buttercream filling, making them fun and easy to eat. They’re perfect for a weekend baking session or a cozy get-together, and they have that nostalgic taste that feels both familiar and a little special.

For another fun spin on whoopie pies, check out our Chocolate Chip Whoopie Pies recipe – a delicious twist on this classic treat with a chocolatey center.

plate of 3 finished whoopie pies.

I’m sure you’ll enjoy it as much as I do.

Tips for the Best Oatmeal Whoopie Pies

  • Once you add the flour, oats, and dry ingredients, mix until everything is combined. Overmixing can make the cookies tough instead of soft and chewy.
  • Use a cookie scoop or a measuring spoon to keep your cookies the same size (which looks nicer for sandwiches). This helps them bake evenly, so each cookie matches well when you combine them. If you want a fruity twist, our Strawberry Whoopie Pies bring fresh berry flavor with each bite.
  • If your dough is too sticky or soft to handle, put it in the fridge for 15–20 minutes. Chilling the dough makes it easier to scoop and shape and helps the cookies keep their form while baking.
  • If the filling is too soft, add a little extra powdered sugar, one tablespoon at a time, to make it firmer. This will help the filling stay put when putting the pies together.
  • Ovens can have hot spots, so turning your baking sheets halfway through baking can help the cookies cook evenly. Swap the top sheet to the bottom and vice versa.
  • Instead of just using a toothpick to check, gently press the center of a cookie. It should feel set and a little springy but not hard. If it’s too soft, let it bake for another minute.
  • If you’re baking at high altitudes, you may need to adjust some ingredients or baking times for the best results. Check out this high-altitude baking guide for tips.
  • If you’re stacking the whoopie pies in a container, put a piece of wax or parchment paper between each layer to stop them from sticking together.

Here are some important ingredients and tools to help make this recipe just right. Each one is important for achieving the right texture and flavor, so here’s what you need:

ingredients on concrete counter.
  • Quick Oats: Quick oats make the cookies softer and lighter than old-fashioned oats. You can find them in the baking aisle but don’t use instant oats, as they will change the cookie’s texture. If you only have old-fashioned oats, you can pulse them in a food processor for a similar texture.
  • Marshmallow Cream: This fluffy spread, often called marshmallow fluff, is key for the filling. It’s usually located near the marshmallows in the baking aisle. You can make your marshmallow fluff if you can’t find marshmallow cream, but it might be a bit softer. While you can make it home, store-bought is quicker and more dependable.
  • Unsalted Butter: Using unsalted butter helps you manage the salt level in the cookies. If you only have salted butter, use less added salt to keep the flavors balanced. You can also use margarine or plant-based butter instead of unsalted butter for a dairy-free option.
  • Whole Milk: Whole milk adds richness and moisture to the cookies. If you need an alternative, 2% milk works, but skip skim or non-dairy options, as they can make the cookies less tender.
  • Parchment Paper: Lining your baking sheets with parchment paper keeps the cookies from sticking and helps them bake evenly. You can find it in the same aisle as aluminum foil and plastic wrap, and it’s great for easy cleanup.
  • Cookie Scoop: A medium cookie scoop allows you to portion the dough evenly, ensuring each whoopie pie is the same size. This leads to even baking and gives your pies a consistent look.

Using these ingredients and tools will greatly improve your results, helping you make whoopie pies that look and taste fantastic!

Serving Suggestions

Serve these pies with hot coffee or tea, a scoop of vanilla ice cream, fresh berries, a glass of cold milk, or a cozy mug of warm apple cider.

Troubleshooting and Help

Can I use instant oats instead of quick oats?

If possible, I’d skip the instant oats, as they’ll make the cookies more dense and heavy. Quick oats give just the right texture, but if you only have old-fashioned oats, pulse them in a food processor a few times to get a similar consistency.

My cookies turned out flat—what happened?

Flat cookies usually mean the butter was too soft or the dough was overmixed. Next time, try chilling the dough for 10–15 minutes before baking to help it hold its shape better.

Can I make the filling ahead of time?

Absolutely! You can make the filling a day in advance. Just keep it covered in the fridge, and when you’re ready to use it, let it sit at room temperature so it softens up for easy spreading. If you’re a fan of traditional Whoopie pies, you’ll love our Vanilla Whoopie Pies – another nostalgic treat with a smooth, creamy filling.

How do I keep the filling from squishing out?

If the filling seems soft, pop it in the fridge for 10 minutes before assembling. Also, be sure the cookies are completely cool before you add the filling. A little chilling after assembly can help set everything up nicely.

How thick should the filling layer be?

It’s really up to you! About ¼ cup of filling per whoopie pie works well, but please add more if you like extra filling. Just know that too much filling might make them harder to eat.

Can I add mix-ins to the cookie dough?

Absolutely, as long as you keep it light! Mini chocolate chips, chopped nuts, or even a handful of raisins can add a fun twist, but be careful not to overdo it—too many add-ins could make the cookies spread too much.

Storage Instructions

To store your whoopie pies, place them in an airtight container. They will keep well in the refrigerator for up to 5 days. Before serving, let them sit at room temperature for a few minutes so the filling softens.

If you’d like to freeze them, wrap each whoopie pie individually in plastic wrap, then place them in a freezer-safe container or zip-top bag. They can be frozen for up to 2 months. When ready to enjoy, let them thaw in the refrigerator or at room temperature until soft.

These pies are a simple, nostalgic treat that’s easy to make and enjoy. With soft, spiced oatmeal cookies and a creamy marshmallow filling, they’re perfect for any occasion, from family gatherings to quiet afternoons at home. Whether you’re sharing them with friends or savoring one solo, these treats will surely become a favorite, and you’ll come back to them again and again.

hand holding whoopie pie.
picture of smiling female

By Katie Shaw

Katie lives in Virginia with her husband, three daughters, a chocolate lab, and over thirty chickens. She loves creating simple tutorials for sourdough, bread, and soap. Her recipes, articles, and YouTube videos reach millions of people per year.

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