Prep. Preheat the oven to 375°F. Line two baking sheets with silicone baking mats or parchment paper.
Cream butter and sugar. In a large bowl, using a mixer, cream 1 cup softened butter, 1 cup brown sugar and 3/4 cup granulated sugar for 1 minute. Add 2 eggs and 2 teaspoons vanilla and mix until combined.
Add dry ingredients then chill dough. Add 3 cups flour, 1 teaspoon baking soda and 1 teaspoon salt and stir mix just until combined. Fold in 1 cup chocolate chips and 1 cup M&M’s. Refrigerate dough for 15 to 60 minutes (up to 24 hours) if time allows.
Scoop dough. 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. 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. Store in an airtight container for up to 3 days.
Notes
Storage:Store in a covered container up to 3 days. Freeze in a covered container up to 3 months.Leftover dough:Form dough into balls and add to baking sheet. Place sheet in freezer until dough has hardened. Remove from freezer and add dough balls to freezer safe container or zip top bag. Store in freezer until ready to bake. Then place on the baking sheet 30 minutes before baking to soften.