Preheat oven to 375. Combine flour, baking soda and salt in a bowl and set aside. Beat butter, sugars and vanilla in a large bowl until cream. Add eggs, one at a time and continue mixing until well combined. Slowly add in your flour mixture. Add in M&M's. Drop by rounded teaspoons (I use a cookie scoop) on an ungreased cookie sheet (I line mine with parchment paper) and bake for about 9-11 minutes. Allow to sit on cookie sheet for 2 minutes to cool, and then transfer them to wire racks. Makes about 5 dozen.