01 -
Whisk flour, baking soda, cornstarch and salt together.
02 -
Melt butter and let it cool until no longer hot. Whisk butter with brown and granulated sugars.
03 -
Add the whole egg, extra yolk and vanilla. Mix in dry ingredients just until no flour streaks remain.
04 -
Fold in chocolate chips and M&Ms.
05 -
Cover and refrigerate at least thirty minutes, longer if still loose. Heat the oven to 350°F and line baking sheets.
06 -
Scoop uniform two-tablespoon portions with room to spread. Bake about ten to twelve minutes, continuing until edges are set and centers are baked.
07 -
Cool on the tray five minutes. Transfer to a rack and cool completely before storing.