In large bowl mix butter, egg, sugar, vanilla and peanut butter until combined. Then add flour and oats stir until combined, Stir in chips and M&M's. If you want it to look pretty save a few chips and M&Ms to sprinkle on the top.
Bake at 350 degrees for 20-22 mins.
Recipe by THE SEMISWEET SISTERS at https://www.thesemisweetsisters.com/2016/05/15/monster-cookie-bars/