Preheat oven to 350F. Line two large baking sheets with parchment paper.
Melt butter in the microwave or on the stovetop. Set aside.
In a medium size bowl, combine flour, baking soda and salt. Whisk to combine.
In a large bowl, add melted butter, granulated sugar and brown sugar. Beat with an electric mixture at medium speed until the butter and sugars are mixed well.
Add eggs and vanilla. Beat with mixer on medium speed until the eggs and vanilla have been mixed in. Use a spatula to scrape down the sides of the bowl.
Add half of the flour mixture. Beat at low speed until the flour mixture begins to incorporate into the dough. Increase the speed to medium and continue to beat until the flour is mixed into the dough. Repeat with remaining flour mixture. Use a spatula to scrape down the sides of the bowl as necessary.
Add M&M's to the cookie dough. Fold in the M&M's using a spatula.
Use a cookie scoop or large spoon to drop cookies dough balls onto prepared baking sheets. Use about 1 ½ tablespoons of dough for each cookie.
Bake for 10-12 minutes or until the tops of the cookies start to turn golden brown. Remove cookies from the oven and let cool for 10 minutes before transferring to a wire rack to cool completely. Makes 30 cookies.