Preheat oven to 350 degrees

Add melted butter, brown sugar and white sugar to a large mixing bowl and mix until well combined.

Beat in vanilla and egg.

In a separate bowl mix together flour, baking soda and salt. Add in 1/3 at a time to wet mixture and stir to combine.

Gently stir in M&M's and reserve a few to press into top of cookie dough

Place on a large ungreased cookie sheet and back approx. 9 minutes. Do not overbake, they will be slightly underdone when removed but will continue to bake as cooling.

Allow to cool for 5 minutes and then transfer to a cooling rack. Store in an airtight container.