For cake ~
1/4 cup butter
1 3/4 cups all-purpose flour
1 cup unsweetened cocoa powder
1 tsp baking soda
3/4 tsp baking powder
1/2 tsp salt
1 cup milk
1/2 cup strong brewed coffee, cooled
2 cups sugar
2 tsp vanilla
1 cup semisweet chocolate, chopped
For frosting ~
1/3 cup butter
4 cups powdered sugar
3 Tbsp strong brewed coffee, cooled
1 tsp vanilla
Allow butter and eggs to stand at room temperature for 30 minutes. Line 30 2 1/2-inch muffin cups with paper liners. Stir together flour, cocoa powder, baking soda, baking, powder, and salt. In a 2-cup measuring glass combine milk and coffee. Set aside.
Preheat oven to 350 degrees Fahrenheit.
In a large bowl beat butter with an electric mixer on medium speed for 30 seconds. Gradually add sugar, about 1/4 cup at a time, beating on medium till combined. Scrape bowl, beat two minutes more. Add eggs, one at a time, beating well after each addition. Beat in vanilla. Alternatively add flour mixture and milk mixture to butter mixture, beating on low speed after each addition just until combined. Stir in chocolate pieces.
Spoon batter into baking cups, filling about three-fourths full. Bake 15-18 minutes, or until tops spring back when lightly touched. Cool in pan on wire rack for 5 minutes, then remove from pans and cool completely on rack.
For frosting, beat butter with an electric mixer on medium speed until smooth. Gradually add 1 cup powdered sugar, beating well. Beat in coffee and vanilla. Gradually beat in remaining 3 cups powdered sugar. If necessary, beat in additional coffee until buttercream reaches a spreading consistency. Pipe or spread on cooled cupcakes. If desired, top cakes with additional cocoa powder and insert a Pirouette cookie.