FOR CAKE:
Cooking spray, for pan
2 boxes white cake mix (plus ingredients called for on box)
12 Oreos, crushed
1 c. semisweet chocolate chips
FOR FROSTING
6 sticks unsalted butter, softened
10 c. powdered sugar
3/4 c. whole milk
1/2 tsp. blue food coloring
Kosher salt
FOR GANACHE:
3/4 c. heavy cream
1 1/2 c. semisweet chocolate chips
chocolate chip cookies, for garnish
Oreos, for garnish
2 Milk Duds, for garnish
Step 1
Make cake: Preheat oven to 350° and line three 9" cake pans with parchment paper. Grease with cooking spray. In a large bowl, prepare cake mixes according to package instructions. Gently fold in Oreos and chocolate chips. Divide among pans and bake until a toothpick inserted into the middle comes out clean, about 25 minutes. Let cool completely.
Step 2
Make frosting: In another large bowl using a hand mixer, beat butter with half the powdered sugar until smooth. Add remaining powdered sugar, ½ cup milk, blue food coloring, and ¼ teaspoon salt and beat until fluffy. If mixture is too stiff, add more milk.
Step 3
Level the top of each cake with a serrated knife to create even layers. Place down one cake and top with a heaping cup of frosting, then top with second cake and repeat with third layer.
Step 4
Using about 1 1/2 cups of frosting, smooth a crumb coat around outside of the cake. Transfer cake to refrigerator until frosting is hardened, 30 minutes to 1 hour.
Step 5
Spread outside of cake with remaining frosting.
Step 6
Make ganache: In a small saucepan over medium heat, heat heavy cream just until it bubbles. Place chocolate chips in a small heatproof bowl and pour over hot heavy cream. Let sit 2 minutes, then whisk until smooth and no clumps remain.
Step 7
Drizzle ganache on top of cake, letting it drip down the sides.
Step 8
Separate two Oreo cookies, leaving frosting on one half. Press one Milk Dud into the frosting of each opened Oreo to make eyes and set cookies in the center of cake.
Step 9
Decorate the bottom edge of cake by alternating pressing in Oreos and chocolate chip cookies.
Step 10
Let ganache set slightly, about 15 minutes, before serving.