Preheat oven to 350F, grease three 6" round baking pans and dust with cocoa powder. Line bottoms with parchment.
Place all dry ingredients into the bowl of a stand mixer fitted with a paddle attachment. Stir to combine.
In a medium bowl whisk all wet ingredients (pour coffee in slowly as not to cook the eggs if very hot).
Add wet ingredients to dry and mix on medium for 2-3 mins. Batter will be very thin.
Pour evenly into prepared pans. I used a kitchen scale to ensure the batter is evenly distributed.
Bake until a cake tester comes out mostly clean. A total of 30-35mins.
Cookie Dough Frosting:
Combine flour and salt in a bowl, set aside.
Beat butter until creamy, add sugars and beat on high until pale and fluffy (approx. 2-3mins). Add vanilla and mix until combined.
Reduce speed to low and slowly add in flour mixture. Mix until just incorporated. Slowly pour in milk. Increase speed to med-high and beat for 2-3 minutes until light and fluffy. Stir in chocolate chips.
Place chopped chocolate and cream into a microwave safe bowl. Stir to combine. Microwave for 20 seconds, stir. Microwave in 10 second intervals, stirring in between, until ganache is smooth and silky. Set aside to cool completely before using on cake.
Place one layer of cake on a cake stand or serving dish. Top with about 2/3 cup buttercream. Repeat with remaining layers. Smooth the outside, chill for 30mins.
Using a teaspoon, drip ganache along the edges then fill in the top. Chill for 15mins.
Top with chopped cookies if desired.
Note: You will have some cookie dough frosting left over. I recommend making Cookie Dough Truffles with the excess. Chocolate Chip Cookie recipe here!