Pre-heat oven to 350 degrees. Line a baking sheet with parchment paper, a silpat, or spray with nonstick baking spray.
Cream butter and sugar until light and fluffy.
Add egg, egg yold, peppermint extract, and green food coloring. Start with 6 drops of food coloring, mix until smooth. Gradually add more food coloring until desired color is reached.
Add flour, baking powder, and salt. Mix until combined.
Roll cookie dough in 1" balls. Place on cookie sheet.
Bake 7-9 minutes. I bake my cookies for 8 minutes and it's perfect. Be sure not to over bake them or they will be dry.
Remove cookies from oven. Let sit on cookie sheet for about 2 minutes. Gently, press chocolate kiss into tops of cookies. Move cookies to a wire rack to finish cooling.