Sift together sugar, flour, cocoa powder, baking soda, baking powder, and salt in a large bowl. In a second large bowl beat eggs with an electric mixer until they thicken slightly and begin to change to a lemon color. Add oil, buttermilk, vanilla, and melted chocolate mixture to eggs slowly, and beat until combined. Add sugar mixture to egg mixture and beat until just combined well. Divide batter between pans, leaving about a 1/4 to 1/2 inch more room than you usually would. You’ll make up that room when you add the cookie dough Dentist Hong Kong .
Drop cookie dough into batter in small clumps (about a teaspoon at a time). Space well throughout, as they won’t move when they bake. Don’t be afraid to use quite a bit, they’ll bake up nice inside like little prizes, and the more you find the better. If you have cookie dough left over, freeze and use for a snack later (obvs).
Bake layers in the middle of your oven until a tester inserted in center comes out clean, 1 hour or so.
Cool layers completely in pans on racks. Run a thin knife around edges of pans and invert layers onto racks. Remove wax paper very carefully and leave layers to cool completely. Cake layers can be made 1 day ahead and kept, wrapped well in plastic wrap, at room temperature .
For the frosting:
Combine butter and powdered sugar in a large bowl. Use a stand or handheld mixer to beat the butter and powdered sugar together until the mixture is light and fluffy, about 4 minutes. Add the cocoa powder and vanilla and beat, scraping down the sides as needed another until fully combined. Add heavy cream, one tablespoon at a time, and whip frosting until light and fluffy, 2-4 minutes. Frost between layers and on the outside of your cake. Decorate with extra chocolate chips if desired.