Chocolate Chip Layer Cake with Chocolate Chip Buttercream

2 1/4 cups all-purpose flour
1/4 cup unsweetened cocoa powder
1 tsp baking soda
1/2 tsp salt
12 oz semi-sweet or dark chocolate chips, divided (regular or mini)
2/3 cup butter, room temperature
1 1/2 cups sugar
3 large eggs
2 tsp vanilla extract
1 1/2 cups coffee (or water)

Chocolate Sour Cream Buttercream -

3/4 cup butter, room temperature
1/2 cup sour cream
3 tbsp cocoa powder
1 – 2 tbsp milk
1 tsp vanilla extract
approx 3 cups confectioners’ sugar
1/3 cup finely chopped chocolate