BEGIN BY MIXING WET INGREDIENTS:
Cream butter and sugars on high for 2-4 minutes. Scrape sides of the bowl. Add egg and egg yolk and vanilla. Beat again on high for 2 minutes. Scrape sides of bowl again.
MIX DRY INGREDIENTS:
Mix all of your dry ingredients in a separate bowl whisking lightly with a fork. Add your oats last!
Mix in your chocolate chips and M&Ms by hand. Chill the dough in the refrigerator for at least 1 hour or over night.
ONCE THE DOUGH IS CHILLED:
Form large balls (about 2 inches), do not flatten them. Bake in the oven at 350°F for approximately 8-10 minutes (check regularly after 7 minutes because each oven is slightly different for cooking times).