In a large bowl or stand mixer, cream together on medium speed the softened butter and both sugars until blended and white and fluffy. Add egg, egg yolk and vanilla extract and blend for another minute until fully blended.
In a medium bowl mix together flour, cocoa powder, baking powder and salt until well mixed.
Mix the flour mixture into the mixture with butter and sugar and mix on low speed until full combined, about 3 minutes. Cover with plastic wrap and refrigerate it for 30 minutes.
While the dough chills, preheat the oven to 350 degrees and Line a baking sheet with parchment paper or spray your pan with non stick spray.
With a medium cookie scoop, roll cookies into 1 inch cookie balls then roll them in sugar till fully covered and place them on the baking sheet with parchment paper spacing them 2 inches apart, then flatten with your fingers to even them out a little, but don’t flatten them too much!
Bake for 8-10 minutes until the edges are set and the middle is soft, they will not look done but they will set once out, don’t over bake!
Remove them from the oven and allow them to cool for 3-5 minutes, then press Hersey Kiss into the middle of the cookie, gently pressing them down. Allow them to cool on the cookie sheet for another 3 minutes before transferring them to a cooling rack to cool for another 5 minutes.
Share warm or store them in an air tight container at room temperature for up to a week, if they last that long!