In the bowl of a stand mixer, add the cubed butter and sugars. Mix until creamed together. Add in whole egg, egg yolk, and vanilla. Mix until combined. Add in flour, salt, baking soda, and baking powder. Mix until combined. Fold in chocolate and mint morsels.
(For thicker cookies, chill the dough for at least 30 minutes before baking.) Preheat oven to 375 degrees. Using a cookie scoop, portion dough onto a parchment-lined baking sheet. Gently flatten cookies for more uniform baking.
Bake 7-9 minutes until lightly brown around the edges and slightly underdone in the middle. Remove from the oven and let cool for a couple of minutes on the baking sheet before transferring to a cooling rack. Cool completely and store in an airtight container.