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 completely. Using a standing mixer, beat the butter, powdered sugar, Hershey cocoa powder, vanilla and whipping 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.