Preheat oven to 350.
Line baking sheets with parchment paper.
Cream together the butter and sugar.
Add in the egg and vanilla until well combined.
In a separate bowl, whisk together flour and cocoa powder
Slowly add flour mixture to the butter mixture by spoonfuls at low speed, frequently scraping down sides.
Dust work area with cocoa powder or flour.
Roll dough to 1/4" thickness.
Cut out gingerbread man shapes and place on baking sheets.
Bake for 8-10 minutes, until set.
Let cookies cool in pan for 3 minutes before transferring to cooling rack to finish cooling.
Mix powdered sugar, milk and corn syrup in a small bowl until smooth.
Transfer to piping bag or zippered bag to pipe skeleton onto cookies.
Try not to get lines too close together so they don't run together.
Allow to sit for at least an hour for icing to get hard.