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Oatmeal Cream Pie Cake

Oatmeal Cream Pie Cake is a tall, nostalgic oatmeal spice layer cake with a thick pillowy marshmallow cream filling that oozes between moist layers. It’s finished with smooth vanilla cream and topped with oatmeal cookie crumbles plus a light powdered sugar dusting.
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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 jar (7 oz) marshmallow fluff
  • 1 tsp vanilla extract
  • 2 tbsp heavy cream
  • 1 Oatmeal cream pie cookies crumbled, for garnish

Equipment

  • 1 sheet pan
  • 1 stand mixer

Method
 

Bake the oatmeal cake layers
  1. Preheat the oven to 350°F and grease two 9-inch round pans. Set aside so the pans are ready when the batter is mixed.
  2. Whisk together all-purpose flour, blended rolled oats, packed brown sugar, cinnamon, baking soda, baking powder, and salt in a mixing bowl. Whisk until the dry ingredients look evenly combined.
  3. Whisk together the eggs, buttermilk, vegetable oil, and vanilla extract in a separate bowl. Keep whisking until smooth and uniform.
  4. Pour the wet ingredients into the dry ingredients and mix until smooth. Scrape the sides and bottom of the bowl to prevent dry pockets.
  5. Divide the batter between the two prepared pans and bake for 28–32 minutes. Bake until a toothpick comes out clean and the tops spring back lightly.
  6. Cool the cakes completely in the pans, then remove and cool fully again if needed. Letting them cool prevents filling from melting or sliding.
Make the marshmallow cream filling
  1. Beat the softened butter until fluffy. Mix on medium speed until the texture looks lighter and smooth.
  2. Add powdered sugar, marshmallow fluff, vanilla extract, and heavy cream. Beat until smooth and spreadable, then stop as soon as it reaches a pipeable, frosting-like consistency.
Assemble and finish
  1. Place one cake layer on a stand or serving plate. Spread the marshmallow cream filling generously over the top all the way to the edges.
  2. Set the second cake layer on top. Frost the outside with the remaining cream until covered and smooth.
  3. Crumble oatmeal cream pie cookies over the top for garnish. Press lightly so the crumbs adhere to the frosting.
  4. Dust with powdered sugar and serve. Slice after frosting for clean layers and visible cream between them.

Notes

For clean slices and maximum filling “ooze,” chill the assembled cake 20–30 minutes before serving, then keep leftovers refrigerated for up to 4 days. Freezing is not recommended because the marshmallow filling and crumbs can change texture. For a lighter option, you can swap half the heavy cream with additional powdered sugar for a thicker consistency, but the flavor will be slightly less rich.