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Oatmeal Cream Pie Cake

Oatmeal cream pie cake is a tall oatmeal layer cake with a thick pillowy marshmallow cream filling oozing between moist layers, then finished with smooth vanilla frosting and oatmeal cookie crumbles. This nostalgic dessert cake bakes up tender and cozy with cinnamon and blended rolled oats.
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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 eggs large
  • 1 cup buttermilk
  • 0.5 cup vegetable oil
  • 1 tsp vanilla extract
For the marshmallow cream filling
  • 0.5 cup butter 1 stick, softened
  • 2 cup powdered sugar
  • 1 can (7 oz) marshmallow fluff
  • 1 tsp vanilla extract
  • 2 tbsp heavy cream
Garnish
  • 1 oatmeal cream pie cookies crumble for garnish
  • 1 tbsp powdered sugar for dusting

Equipment

  • 2 sheet pan

Method
 

Bake the oatmeal cake layers
  1. Preheat oven to 350°F and grease two 9-inch round pans. This ensures the cake releases cleanly after baking.
  2. Whisk together all-purpose flour, blended fine rolled oats, packed brown sugar, cinnamon, baking soda, baking powder, and salt in a large bowl. Mix until the dry ingredients look evenly speckled.
  3. Whisk eggs, buttermilk, vegetable oil, and vanilla extract together in a second bowl. Stop when the mixture is smooth and uniform.
  4. Combine the wet ingredients with the dry ingredients and mix until smooth. Scrape the sides as needed so there are no dry pockets.
  5. Divide batter between the two pans and bake 28-32 minutes at 350°F, until a toothpick comes out clean. Look for domed tops that spring back lightly when touched.
  6. Cool the cakes completely in the pans, then cool fully before assembling. Letting them cool prevents the filling from melting out.
Make the marshmallow cream filling
  1. Beat softened butter until fluffy. The mixture should lighten in color and look airy.
  2. Add powdered sugar, marshmallow fluff, vanilla extract, and heavy cream, then beat until smooth and spreadable. Pause to scrape the bowl so the frosting stays uniform.
Assemble and finish
  1. Place one cake layer on a stand and spread the marshmallow cream filling generously over the top. Spread to the edges so it can ooze between layers.
  2. Place the second cake layer on top and frost the outside with the remaining cream. Smooth the surface so the crumb peeks through only slightly.
  3. Crumble oatmeal cream pie cookies over the top for garnish. Press lightly so the crumbles adhere to the frosting.
  4. Dust with powdered sugar and serve. Use a light shake for an even, fine finish.

Notes

For clean slices, assemble only after the layers are completely cool (about 1 hour at room temperature). Store covered in the refrigerator up to 4 days; freeze assembled cake slices up to 2 months for best texture. For a lighter option, use a reduced-fat cream cheese-style frosting swap is not directly equivalent here—best swap is substituting the butter with plant butter that measures 1:1.