In a large bowl, cream butter, brown and granulated sugars together until fluffy. Add in the eggs and vanilla. Mix until just combined.
In a separate bowl, whisk together the flour and baking soda. Turn the mixer on low and gradually add the dry ingredients to the wet ingredients until just combined.
Fold in the semi-sweet chocolate chips and M&Ms. Refrigerate the dough for 30 minutes.
Preheat the oven to 375°F. Line two cookie sheets with parchment paper.
Scoop cookie dough onto cookie sheets using a medium cookie scoop or measure out dough, 2 Tbsp. for each cookie. Place 2 inches apart.
*Add 2-3 extra M&Ms on top of each cookie.
Bake the cookies for 8-10 minutes until the edges of the cookies begin to turn golden brown. Cool the cookies on the sheets for 2 minutes to allow for carryover cooking.
Transfer the cookies to wire racks to cool completely. Makes 24-30 cookies.
Notes
*Adapted from Best M&M Cookies - https://www.iheartnaptime.net/best-mm-cookies/