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Oatmeal Cream Pie Cake

Oatmeal cream pie cake is a tall, nostalgic layer cake with a moist oatmeal-spice crumb and a thick pillowy marshmallow cream filling that oozes between layers. Finished with a smooth vanilla cream frosting and oatmeal cream pie cookie crumbles.
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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 softened (1 stick)
  • 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
  • 1 tbsp powdered sugar for dusting

Equipment

  • 2 sheet pan
  • 1 stand mixer

Method
 

Bake the oatmeal spice cake layers
  1. Preheat the oven to 350°F, grease two 9-inch round pans, and set aside. This prevents sticking so the layers release cleanly.
  2. Whisk together the all-purpose flour, blended fine rolled oats, brown sugar, cinnamon, baking soda, baking powder, and salt until evenly combined. Break up any brown sugar lumps for a smooth crumb.
  3. Whisk together the eggs, buttermilk, vegetable oil, and vanilla extract in a separate bowl until uniform. Ensure no streaks of egg remain.
  4. Pour the wet ingredients into the dry ingredients and mix until smooth. Scrape the bowl so the batter bakes evenly.
  5. Divide the batter between the two prepared pans and bake for 28–32 minutes at 350°F, until a toothpick comes out clean. Let the cakes cool completely before assembling.
Make the marshmallow cream filling
  1. Beat the softened butter until fluffy. This creates a lighter base for the filling.
  2. Add the powdered sugar and beat until combined. The mixture should look thick and smooth.
  3. Beat in the marshmallow fluff, then add the vanilla extract. Mix until the filling is airy and no streaks remain.
  4. Beat in the heavy cream until smooth and spreadable. The filling should ooze easily when spread.
Assemble and finish
  1. Place one cake layer on a stand and spread the marshmallow cream filling generously over the top. Aim for an even layer so it puffs between tiers.
  2. Place the second cake layer on top and frost the outside with the remaining cream. Smooth the edges so the dark cake layers stay crisp and visible.
  3. Crumble oatmeal cream pie cookies over the top for garnish. Press lightly so the crumbles adhere.
  4. Dust with powdered sugar and serve. Slice to show the creamy filling between the moist layers.

Notes

Pro tip: cool the cake layers completely before assembling so the marshmallow cream stays thick and doesn’t melt. Store covered in the refrigerator up to 4 days; freeze assembled cake only if necessary (best within 1 month) since cookie topping can soften. For a dietary swap, use a plant-based butter stick and verify marshmallow fluff is egg-free if needed.