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Oatmeal Cream Pie Cake

Oatmeal cream pie cake is a tall oatmeal spice layer cake with a thick pillowy marshmallow cream filling oozing between moist layers, then frosted in smooth vanilla cream and topped with oatmeal cookie crumbles. This nostalgic dessert cake bakes in two 9-inch rounds for an easy-to-slice Little Debbie-style layer cake.
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Prep Time 30 minutes
Cook Time 30 minutes
cooling 1 hour
Total Time 2 hours
Servings: 12 servings
Course: Dessert
Cuisine: American
Calories: 520
Ingredients Equipment Method Notes

Ingredients
  

For the oatmeal cake
  • 2 cup all-purpose flour
  • 1.5 cup rolled oats, blended fine
  • 1.5 cup brown sugar, packed
  • 2 tsp cinnamon
  • 1 tsp baking soda
  • 1 tsp baking powder
  • 0.5 tsp salt
  • 3 large eggs
  • 1 cup buttermilk
  • 0.5 cup vegetable oil
  • 1 tsp vanilla extract
For the marshmallow cream filling
  • 0.5 cup butter, softened
  • 2 cup powdered sugar
  • 1 can (7 oz) marshmallow fluff
  • 1 tsp vanilla extract
  • 2 tbsp heavy cream
  • 1 oatmeal cream pie cookies, crumbled, for garnish

Equipment

  • 2 sheet pan
  • 1 stand mixer

Method
 

Bake the oatmeal spice cake
  1. Preheat oven to 350°F and grease two 9-inch round pans. Set pans aside so the batter goes in right away.
  2. Whisk together all-purpose flour, blended fine rolled oats, brown sugar, cinnamon, baking soda, baking powder, and salt in a bowl. Mix until the dry ingredients are evenly combined.
  3. Whisk together large eggs, buttermilk, vegetable oil, and vanilla extract in a bowl. Whisk until the wet mixture looks uniform.
  4. Combine the wet mixture into the dry mixture and mix until smooth. Stop mixing once no dry streaks remain.
  5. Divide batter between the two greased pans and bake for 28-32 minutes at 350°F, until a toothpick comes out clean. Look for domed tops and light browning at the edges.
  6. Cool completely before assembling the cake layers. This prevents the marshmallow cream filling from melting and sliding.
Make the marshmallow cream filling and frost
  1. Beat softened butter until fluffy. Continue beating until the texture looks lighter and smoother.
  2. Add powdered sugar, marshmallow fluff, vanilla extract, and heavy cream. Beat until the filling is smooth and spreadable.
  3. Place one cake layer on a stand and spread the cream filling generously over the top. Leave a small border near the edge so it doesn’t overflow too aggressively.
  4. Place the second cake layer on top and frost the outside with the remaining cream. Use a flat edge to smooth for an even coat.
  5. Crumble oatmeal cream pie cookies over the top for garnish. Press lightly so the crumbs adhere to the frosting.
  6. Dust with powdered sugar and serve. Cut slices and show the cream filling nestled between the moist oatmeal layers.

Notes

For clean, picture-ready slices, cool the cake layers completely before frosting and assemble at room temperature so the marshmallow cream stays thick. Store covered in the refrigerator up to 4 days; the texture firms when chilled but softens slightly as it sits. Freezing is not recommended because the marshmallow cream filling can lose its smooth, pillowy texture after thawing. If you want a gluten-friendly swap, use a 1:1 gluten-free all-purpose flour blend and keep the blended rolled oats fine for similar structure.