In the bowl of a stand mixer fitted with the paddle attachment, cream together butter, brown sugar, and granulated sugar until combined. Add eggs in one at a time, beating completely after each is added. Beat in vanilla. Add salt, baking soda, and baking powder and beat until combined. Gradually add in flour until fully incorporated. Fold in M&Ms and mini chocolate chips.

Cover the bowl with plastic wrap and chill in the refrigerator overnight.

When ready to bake, preheat oven to 350 degrees. Line 2 large baking sheets with silpats or parchment paper.

Using a Tbsp to measure out each ball of dough, roll each Tbsp of dough into a smooth ball. Space the balls of dough approximately 1” apart from each other on the baking sheet. Press in additional M&Ms on the tops if desired.

Bake for 10 to 11 minutes, until just golden brown on the edges. Cool on the baking sheets for 3 minutes before transferring to cooling racks to cool completely. Repeat the baking process with the remaining dough.