Preheat the oven to 375°F. Line two baking sheets with silicone baking mats or parchment paper.
In a large bowl, using a mixer, cream together the butter and sugars for 1 minute. Add the eggs and vanilla and mix until combined.
Add the flour, baking soda and salt and stir mix just until combined. Fold in the chocolate chips and M&M’s. Refrigerate dough for 15 to 60 minutes (up to 24 hours) if time allows.
Using a large cookie scoop (about 3 Tablespoons), scoop the cookie dough onto the baking sheet about 2 inches apart. Place extra M&M’s on the top of the cookies if desired.
Bake for 7-10 minutes, or until the edges are barely golden brown. Allow cookies to set on pan for 2 minutes, and then remove to a cooling rack.