Preheat the oven to 350 degrees and line two cookie sheets with a silicone baking mat
Using a standing mixer, beat the butter, sugar, light brown sugar, eggs, corn syrup, and vanilla until light and fluffy
Using a medium bowl, whisk the flour, cocoa powder, cornstarch, salt, and baking soda
Gradually beat the dry ingredients into the wet until a dough forms
Using a medium cookie scoop, scoop out the dough mound into your hand and roll it into a ball
Place onto the cookie sheet and lightly press into a thick disk
Bake in the oven for 15-18 minutes or until firm around the edge
Allow cooling completelyUsing a standing mixer, beat the butter, powdered sugar, Hershey cocoa powder, vanilla andwhipping cream until combined, smooth, and holds a peak
Scoop the frosting into the piping bag
Pipe a tight spiral onto the top of the cookie
Allow hardening slightly before enjoying