Cream together the butter, sugar, and brown sugar, then mix in the egg, egg yolk, and vanilla.
Add in the flour, baking soda, salt, mini chocolate chips and mini m&ms and fold until just combined.
Scoop into large dough balls (3 tbsp) and chill the dough until solid. Then bake at 350 for 12 minutes.
Press more mini chocolate chips and m&ms into the cookies right after baking.