Sourdough Lemon Sheet Cake with Lemon Buttercream

A bright, sunny lemon sheet cake that transforms your sourdough discard into a bakery-worthy dessert the whole family will love.

Prep Time15

Cook Time35

Total Time50

Course: Dessert

Keyword: sourdough lemon sheet cake, Spring

Servings: slices

Calories: 373kcal

Author: Katie

Equipment

stand mixer or hand mixer
Large mixing bowl
saucepan
13x9 inch baking pan

Ingredients

Cake

2 cups all-purpose flour
1 teaspoon salt
1½ teaspoons baking powder
½ teaspoon baking soda
4 large eggs
1¾ cups sugar
¾ cup sourdough discard 100% hydration, at room temp
¾ cup milk
¼ cup butter room temperature (cut into tablespoon pieces)
⅓ cup vegetable oil
2 tablespoons lemon zest
1½ tablespoons lemon juice
2-3 drops yellow food coloring optional

Lemon Buttercream

1 cup unsalted butter softened (2 sticks)
4 cups powdered sugar
1½ tablespoons lemon zest
2 tablespoons fresh lemon juice
2 tablespoons heavy cream
Pinch salt
Additional lemon slices or zest for garnish

Instructions

Prep. Preheat your oven to 325°F with a baking rack in the center. Grease your 13x9-inch pan with non-stick spray.
Mix Dry Ingredients. In a medium bowl, whisk together the flour, salt, baking powder, and baking soda.
Beat Eggs & Sugar. In your stand mixer bowl or another large mixing bowl, beat the eggs and sugar at medium-high speed for 2–3 minutes until the mixture is very light and fluffy.
Add Sourdough Starter. Gently mix in the sourdough discard until just combined.
Combine Dry & Wet. Add the dry ingredients to the egg mixture and beat until just incorporated—scraping down the sides if needed.
Heat the Milk Mixture. In a small saucepan, heat the milk with the vegetable oil and butter until it's just beginning to simmer. Remove from the heat.
Fold In Milk & Lemon. Gently fold the warm milk mixture into the batter. Then, stir in the lemon juice, lemon zest, and food coloring if using.
Bake. Pour the batter into your prepared pan and bake for 30-35 minutes. (The cake might look a bit spongy—that's normal.) Test with a toothpick; it should come out clean.
Cool. Allow the cake to cool completely in the pan before frosting.
Make the Lemon Buttercream. Beat the butter, powdered sugar, lemon zest, lemon juice, salt, and 1 tablespoon heavy cream in your stand mixer. Add a bit more cream if needed until you reach your desired frosting consistency.
Assemble. Spread the buttercream evenly over the cake. Top with thin lemon slices or lemon zest curls. Serve straight from the pan, and store any leftovers in an airtight container in the fridge.

Video

Notes

Sourdough Flavor: The discard adds a slight tang that complements the lemon. If your starter is very tangy, you might adjust the lemon juice to taste.
Baking Time: Because a 13x9 pan makes a slightly thicker cake than a jelly roll pan, your bake time will likely be shorter than the original. Start checking at 25 minutes.
Storage: The cake stays delicious for up to a week in the fridge. It also freezes well if wrapped tightly.
Make Ahead: You can bake the cake a day ahead and frost it just before serving.

Nutrition