In a medium bowl, whisk together flour, cocoa powder, baking soda, baking powder, and cornstarch.
In a second mixing bowl, cream together the butter, granulated sugar, and brown sugar until light and fluffy (about 2 minutes on medium speed). Add the eggs and vanilla (or mint) and beat until combined.
With the mixer on low, gradually add the flour mixture and beat just until combined.
Cover dough with plastic wrap and chill for 1 hour in the refrigerator.
Preheat the oven to 350 degrees and line baking sheets with parchment paper.
Use a cookie scoop to form 1 ½ tablespoon balls of dough. Roll in a small bowl with the powdered sugar to coat the ball. Place about 2 inches apart on prepared cookie sheets.
Bake for 8 to 9 minutes and remove from the oven. Press one unwrapped Hershey’s kiss into the center of each cookie as soon as they come out of the oven.
After 2 minutes, when the Hershey’s kiss has softened through, lift and discard the tip from each kiss so that the chocolate will puddle into the cookie.
Transfer cookies to a cooling rack and allow them to cool.
Oven temperatures vary and may need to be recalibrated periodically to ensure they are accurate. Make sure to check your cookies at the lower end of the recommended baking time.
I like to roll the powdered sugar on nice and thick so that the crackle effect is really evident. A light dusting of powdered sugar may get absorbed into the cookie.
Work quickly to put the Hershey’s kisses into the cookies as soon as they come out of the oven. Unwrap them before the cookies come out of the oven. The Hershey’s kisses won’t change in shape as they melt - look for a glossy sheen all over the kiss and then pull the tip off.
You can alternately wait until the Hershey’s kisses are soft and use a toothpick to swirl the chocolate into a “puddle.”