In a medium bowl, combine the flour, salt, and baking soda. Set aside.
Beat the butter, granulated sugar, brown sugar, and vanilla in a large mixer bowl until creamy.
Add the eggs, one at a time, beating well after each addition. Gradually add in the flour mixture.
Stir in the chocolate chips and M&M's.
Drop by rounded tablespoon using a cookie scoop onto baking sheets lined with parchment paper.
Bake for 9-12 minutes or until golden brown.
Cool on the baking sheet for 2 minutes, then transfer the cookies to wire racks to cool completely.
Notes
Chill the dough at least 30 minutes before baking to get the butter in the dough cold again. This will help the cookies keep their shape and not spread while baking.