In a mixing bowl, whisk together the flour, baking soda, and salt until well combined.

In another bowl, beat the butter, granulated sugar, and brown sugar with your electric mixer on medium speed for about 3-5 minutes.

Mix in the vanilla extract and eggs one at a time until fully incorporated.

Gradually add the dry ingredients to the wet mixture, mixing on low speed until just combined.

Gently fold in the M&Ms and semi-sweet chocolate chips.

Cover the dough with plastic wrap and refrigerate for 30 minutes to 24 hours.

Preheat your oven to 375°F (190°C) and line two baking sheets with parchment paper.

Scoop rounded tablespoons of dough onto the prepared baking sheets, spacing them 2 inches apart. Press a few extra M&Ms on top if desired, and bake for 9-11 minutes.

Let the cookies cool for a few minutes on the baking sheets before transferring to a wire rack.