How to Make It
Preheat oven to 400°F. Whisk together flour, baking powder, baking soda, and salt in a medium bowl.
Beat together butter and sugars with an electric mixer at medium speed, until fluffy, scraping down sides of bowl as needed. Add eggs and vanilla, and beat until pale, about 4 minutes.
Reduce speed to low, and gradually add flour mixture until just blended. Fold in M&M’s.
Place 2-tablespoon portions per cookie, 2 inches apart on parchment-lined baking sheets (6 cookies per baking sheet). Chill dough on baking sheets 1 hour. Bake in preheated oven until cookies brown on edges, 8 to 10 minutes, rotating halfway through. Cool on baking sheets 5 minutes before transfering to a cooling rack.