Cream the butter and sugars together. Add vanilla and mix well. Add eggs, one at a time, mixing well after each.
Sift together the bread flour, baking soda, and salt. Slowly add mixture to butter mixture and mix until combined.
Add in M&M's and chocolate chips and mix in.
Allow to chill for approximately 4 hours. Bake on parchment paper at 350 for 10-11 minutes, or until the edges are JUST turning brown. Do not over bake or you will have hockey puck cookies! Adjust time as necessary.
Recipe by Smidge of Delish at https://smidgeofdelish.com/mm-cookies/