Preheat the oven to 400°F.
Whisk together the dry ingredients in a large bowl: All-Purpose flour, cake flour, corn starch, baking soda, baking powder and salt. Set aside.
1 1/4 cup All-Purpose Flour, spooned and leveled, 3/4 cup Cake flour, spooned and leveled, 1 tsp. cornstarch, 1/2 tsp. baking soda, 1/2 tsp. baking powder, 1/2 tsp. salt
Using a stand mixer fitted with the paddle attachment, cream together the butter and sugars. Then add in the egg, egg yolk and vanilla extract. 1/2 cup cold, unsalted butter, cubed, 1/2 cup brown sugar, packed (light or dark), 1/4 cup granulated sugar, 1 large egg, 1 large egg yolk (no whites), 1 tsp. vanilla extract
Gradually add in the dry ingredients followed by the chocolate chips. Turn off the machine.
3/4 cup chocolate chips (semi-sweet, milk chocolate, dark or whatever you prefer!)
Stir in the mini m&ms with a rubber spatula.
1 cup mini M&Ms
Form the dough into 6 large dough balls and place on a cookie sheet. You can use a silicone baking mat or parchment paper if you prefer.
Bake for 10-12 minutes, or until tops of cookies are golden brown. Ovens may vary.
Cool on the baking sheet for 15 minutes then transfer to a cooling rack to cool completely.*