Preheat oven to 350 degrees F and prepare cake batter as directed on package.
Using a standard muffin/cupcake tin put a sheet of foil over whole pan, securing it around edges.
Using a knife or skewer, poke a hole in foil above each muffin cup. Gently enlarge hole until ice cream cones just fit through it.
Repeat for all cones. Your cones should now be supported by the foil.
Fill cones two-thirds full with cake batter and bake 18 to 20 minutes or until toothpick inserted into cake comes out clean.
As soon as cones come out of oven, use a skewer or toothpick to poke 3 holes in bottom of cone to let steam and moisture escape.
Cool cones completely.
Pour 1 packet of Duncan Hines(R) Frosting Creations(TM) Chocolatey Mint Flavour Mix into 1 can of Duncan Hines(R) Frosting Creations(TM) Frosting Starter. Stir until evenly blended. Repeat with second can and packet.
Mix the chopped chocolate into the Chocolatey Mint frosting you just created and transfer frosting to a piping bag with an open star decorator tip.
Pipe the frosting in a swirling motion around your cones and serve.