Preheat oven to 350 degrees. Line two cookie sheets with parchment paper and set aside.
Chop Mint Truffle Hershey Kisses in half. Set aside as you make the cookie dough.
In a large bowl, whip butter and sugar until light and fluffy.
Stir in egg and vanilla and beat until pale yellow, 2 minutes.
Gently stir in all dry ingredients until just incorporated. Scrape sides and mix again.
Fold in chopped Mint Truffle Hershey Kisses.
Drop by the tablespoon full onto prepared cookie sheets (about 8 cookies per sheet). Bake 8-9 minutes. The edges should be set with slightly soft middles.
Remove from oven, cool 3 minutes on the hot cookie sheets, then transfer cookies to a cooling rack.