Melt butter in the microwave.
Stir in both sugar until smooth.
Add egg and yolk and vanilla.
Stir in flour, cornstarch, salt and baking soda.
Fold in chocolate chunks and chill for several hours.
Preheat oven to 325 and bake medium sized scoops for 8-10 minutes.
Immediately, sprinkle cookies with chopped Heath bars when you pull the tray out of the oven. Let them cool on tray before removing.