1Preheat oven to 350-degrees. Line 24 muffin cups with paper liners.
2In a medium saucepan, combine butter, cocoa, chocolate and espresso powder. Cook over low heat, stirring constantly, until chocolate melts and mixture is smooth. Let cool for 20 minutes.
3In a large bowl, beat sugar and eggs at medium-high speed with a mixer until fluffy. In another medium bowl combine flour, salt, baking powder and baking soda.
4Gradually add to sugar mixture, beating until combined. Add chocolate mixture, stirring until smooth. Stir in sour cream.
5Spoon batter into prepared muffin cups, and bake for 12-14 minutes or until a wooden pick inserted into the center comes out clean. Let cool in pan for 10 minutes. Remove from pan, and cool completely on wire racks. Pipe Creamy Espresso Frosting over each cupcake.
In a large bowl, combine cream and espresso powder, stirring until espresso powder dissolves.
7Add butter and beat at medium speed with a mixer until creamy. Gradually add powdered sugar, beating until smooth. Pipe frosting on cupcakes.