Step 1

Preheat oven to 350°F, with a rack in the middle position

Step 2

Line a 9-by-13-inch baking pan with a piece of parchment paper long enough to leave overhang on two sides to help remove the baked cookie

Step 3

Use a cheese grater to grate the cold butter directly into a stand mixer bowl

Step 4

Cream the butter and both sugars for 2 minutes on medium-high speed until fluffy and lighter in color

Step 5

Add the egg and egg yolk, along with the vanilla

Step 6

In a separate bowl, whisk together or sift the flour, cornstarch, salt, baking soda and baking powder

Step 7

Add the dry ingredients to the wet ingredients and mix on low speed just until combined

Step 8

Add the chocolate chips and gently mix; do not overmix

Step 9

Press the dough evenly into the prepared baking pan, then smooth the top to create an even surface

Step 10

Bake for 25 to 30 minutes

Step 11

The cookie should be nice and soft, but cooked through with golden brown edges

Step 12

Don't overbake

Step 13

Use an offset spatula to gently press down on the cookie to create a flat surface and smooth the edges

Step 14

Let cool in the pan completely to firm up, then remove by pulling up on both sides of the parchment paper overhang

Step 15

Discard parchment and set the cookie on a rectangular cake board or platter

Step 16

Decorate according to the touchdown theme, as desired