Preheat the oven to 400 degrees. Cut the cold butter into small chunks and add it to a bowl with both sugars. Beat for a couple minutes until it is lighter and smooth.
Add the egg and egg yolk and mix again. Add the cocoa powder, flour, salt, baking powder, and baking soda. Mix just until combined.
Cut the Hershey’s Gold bars into small chunks. Grab a large piece of dough (6 oz, if you have a kitchen scale) and flatten it in your hand. Add a large handful of the chunks of Hershey’s Gold and close the dough around it.
Bake the cookies at 400 degrees for 8-11 minutes, until the outside is set. Let cool completely. If you are adding gold leaf on top, pat the cookie with a damp paper towel, then carefully put the gold leaf on top. Enjoy your treasure hunt cookies!!
