In a bowl mash the butter and sugars together until thick and combined
Mix in the egg, yolk and vanilla
Add flour, cornstarch, baking soda, baking powder, and salt
Mix until just combined
Fold in chocolate chunks
Divide into 6-8 large cookie mounds, keeping them tall and rough
Chill the dough balls 30-45 minutes
Bake at 400°F (205°C) for 10-13 minutes until the edges are golden but the center is still soft
Let them rest on the pan 10-15 minutes before moving
