Preheat the oven to 400° F. Prepare your cookie sheet by placing a silicone liner on it and then stacking a second cookie sheet underneath your first one, creating a double layer with the silicone liner on the top cookie sheet. Set aside.
In a bowl, whisk together the butter, brown sugar and granulated sugar until completely incorporated.
Add in the egg yolk and vanilla, stirring well.
Using a silicone spatula, add in the flour, cornstarch, baking powder and salt. Mix until a dough forms. You may need to finish the mixing with your hand to get all of the flour completely incorporated.
Mix in the chocolate chips.
Gather the dough and roll into either one giant ball or split the dough into two equal sized, smaller, cookies.
Pinch and dimple the dough before placing it on a silicone lined cookie sheet.
Bake at 400° F until the cookie is golden brown across the top of the cookie. For one large cookie, it will be about 12-14 minutes, for the smaller cookies it will be about 8-10 minutes.
Allow the cookie to set up and cool on the hot pan for 20-25 minutes before enjoying.