Preheat oven to 350 degrees F. Line a baking sheet with parchment paper. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, beat the butter, sugar, brown sugar, peanut butter, egg, and vanilla together until fluffy.

Slowly add the dry ingredients to wet mixture, beating until well blended. Fold in the one cup M&M candies. Reserve the 1/3 cup for placing on top when they come out of the oven.

Drop a tablespoon of dough onto the prepared baking sheet. Bake 12 minutes until lightly browned.

Immediately after removing from the oven, carefully press 2-3 pieces of M&M's candies to the top of the cookies. Place the cookies onto a wire rack to cool completely.