Preheat oven to 350 degrees. Line muffin cups with paper liners. Sift flour, baking soda, salt, and cocoa. Set aside. Cream butter and sugar until light, about 5 minutes. Add eggs, one at a time, beating well after each addition. Beat in peppermint extract. Slowly blend in flour mixture, alternating with milk, until blended. Spoon batter into paper liners, filling each cup three-fourths full.

Bake 12-15 minutes, or until cake tester inserted in center comes out clean. Do not overbake. Cool cupcakes in pan on a wire rack 5 minutes. Remove cupcakes to wire rack to cool completely. Melt chocolate and butter in a medium saucepan over low heat. Stir until smooth. Remove saucepan from heat and stir in peppermint extract. Cool frosting until spreadable. Frost cupcakes. Yields 20 cupcakes.