Ingredients

• For the Cake:
• 3 cups cake flour
• 3/4 cup uncooked oatmeal
• 2 tsp. baking powder
• 1 tsp. baking soda
• 1/2 tsp. salt
• 1 cup unsalted butter, at room temperature
• 1 cup light brown sugar, firmly packed
• 1/2 cup granulated sugar
• 2 TBSP molasses
• 2 tsp. vanilla extract
• 3 large eggs
• 2 large egg yolks
• 1 cup plus 2 TBSP full fat buttermilk
• For the Filling: (not a huge fan, next time try SMBC)
• 1 cup shortening
• 1 cup powdered sugar
• 1 (7oz) jar marshmallow fluff
• 1 1/2 tsp. Vanilla extract
• For the Crumbles: (huge amount of crumbles!)
• 1 (17.5 oz) Oatmeal Cookie Mix (I used Betty Crocker)
• 1/2 cup unsalted butter, melted

Instructions

1. For the Cake:
2. Preheat oven to 350°F.
3. Grease and flour three 6 inch pans and set aside.
4. Sift together the flour, oatmeal, baking powder, baking soda, and salt set aside.
5. In the bowl of a stand mixer fitted with a paddle attachment, beat the butter on medium speed until smooth.
6. At the sugars and mix on medium high until the butter is light and fluffy, about three minutes.
7. Stop the mixer and scrape down the bowl.
8. The mixer to medium low and add the molasses, vanilla, and the eggs and egg yolks, one at a time until combined.
9. Stop mixer and scrape down the bowl.
10. Turn the mixer to low and add the flour mixture in three batches, alternating with the buttermilk, beginning and ending with the flour mixture.
11. Mix on medium for no more than 30 seconds after the last streaks of dry ingredients are combined.
12. Evenly divided the batter between the prepared pan.
13. Bake for 30 to 35 minutes or until a toothpick inserted into the center of the cakes comes out clean.
14. Let them cool on wire rack for 10 to 15 minutes before removing the cakes from their pans.
15. Keep the oven at 350F for the crumbles.
16. For the Crumbles:
17. Mix together the cookie mix and melted butter. 
18. Mix with your hands until crumbles form.
19. Spread out the mixture onto a baking pan lined with parchment paper.
20. Bake for 10 minutes. 
21. Then flip the crumbles with a spatula and bake another 5-10 minutes depending how crunchy you want your crumbles to be.
22. For the Filling: 
23. Cream the shortening, powdered sugar, and vanilla together until smooth.
24. Add the marshmallow fluff and mix until fully combined. 
25. Putting the cake together:
26. Place a cake layer on a cake pan. 
27. Take 1/3 of the filling and spread it on top of the layer.
28. Add 1/2 cup of crumbles.
29. Repeat until all the filling and cake layers are gone. 

Swiss Meringue Buttercream Recipe

 Prep Time 25 minutes  Cook Time 5 minutes  Total Time 30 minutes

Ingredients

• 5 large (150 grams) egg whites
• 1 1/4 cups (250 grams) granulated sugar
• 3 sticks (340 grams) unsalted butter, at room temperature
• 2 teaspoons pure vanilla extract
• 1/4 teaspoon fine salt

Directions

1. Wipe the bowl of an electric mixer with paper towel and lemon juice or vinegar to remove any trace of grease. Make a double boiler by placing the mixer bowl over a saucepan of simmering water, making sure the bowl doesn’t touch the water.
2. Add the egg whites and sugar to the bowl, whisking constantly but gently, until temperature reaches 140°F, or until the sugar has completely dissolved and the egg whites are hot.
3. Attach the bowl to the mixer fitted with the whisk attachment and begin to whip until the meringue is thick, glossy, and the bottom of the bowl no longer feels warm, about 7 to 10 minutes.
4. Switch over to paddle attachment and, with mixer on low speed, add the butter cubes, one at a time, until incorporated. Continue beating until it has reached a silky smooth texture. If the buttercream curdles simply keep mixing and it will come back to smooth. If the buttercream is too thin and runny, refrigerate for about 15 minutes before continuing mixing with paddle attachment until it comes together. Add the vanilla and salt, continuing to beat on low speed until well combined.
5. Add additional flavors, purees, or mix-ins as desired.

To make ahead:

1. Keep in airtight container in refrigerator for up to one week or in the freezer for up to 2 months. Let come to room temperature and rewhip in the mixer with the paddle attachment before using.

Recipe Notes

This makes enough frosting to generously frost a 9-inch two layer cake or about 2 dozen cupcakes. This recipe can easily be doubled.