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!

Oatmeal Whoopie Pies
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
- 1½ teaspoons cinnamon
- 1 teaspoon baking soda
- 1 teaspoon baking powder
- 1 teaspoon salt
- ½ cup milk whole preferred, but 2% is okay
- 1½ quick oats not instant
- 1½ 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.
- 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.
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.
- 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.
Notes
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.

I’m sure you’ll enjoy it as much as I do.
Key Ingredients and Tools
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:

- 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!
Troubleshooting and Help
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.
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.
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.
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.
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.
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.
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.


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.