Sift together flour, granulated sugar, cocoa, soda, and salt in a large bowl. Combine coffee and 1/2 cup butter in a small saucepan; cook over medium heat until butter melts. Gradually add coffee mixture to flour mixture, beating at medium speed with an electric mixer until combined. Add egg, and beat until blended.
Spoon batter evenly into 6 lightly greased jumbo muffin pans. Bake at 350° for 23 minutes or until a wooden pick inserted in center comes out clean. Cool in pans on a wire rack 20 minutes; run a knife around edges of each muffin pan to loosen cakes. Invert cakes onto a wire rack, and cool completely.
Beat 1/4 cup butter and mascarpone cheese at medium speed until creamy; gradually add 2 cups powdered sugar and extract, beating until smooth.
Split cooled cakes in half horizontally. Spread cheese mixture between layers and on top and sides of each cake. Freeze cakes 15 minutes.
Meanwhile, combine cream and 1/4 cup mint leaves in a 2-cup glass measuring cup. Microwave at HIGH 1 to 1 1/2 minutes or until mixture boils. Pour mixture through a wire-mesh strainer into a small bowl, discarding mint. Add morsels, stirring until melted.
Pour ganache over cakes, coating tops and sides. Chill 1 hour or until set. Dust cakes with powdered sugar; garnish, if desired. Store in refrigerator.
Note: If you don't already own a jumbo muffin pan, this recipe is worth the investment--which doesn't have to be much. Jumbo muffin pans are readily available in a variety of stores from discount super centers to specialty kitchen shops. In addition to creating an assortment of miniature cakes, you can use this pan to make wonderful jumbo bakery-style breakfast muffins. This recipe does not work in regular-size muffin pans.