In a small bowl, whisk together flour, cornstarch, cocoa powder and salt.
In a large bowl, cream together butter and sugar. With the mixer on low speed, add in the milk and the extracts. .
Add in the flour mixture until fully incorporated.
Shape dough into two logs, wrap in plastic wrap and freeze for at least 1-2 hours, until dough is very firm.
Preheat oven to 375 degrees
Slice dough into rounds not more than 1/4 inch thick – if they are too thick, they will not be as crisp – and place on a parchment lined baking sheet.
Bake for 13-15 minutes, until cookies are firm at the edges. Cool cookies completely on a wire rack before dipping in chocolate.
Once cookies are cool, melt your bag of candy melts and pipe icing on top of cookies.