Heat the butter in a saucepan until it is all melted. (The butter should smell nice and nutty.)
Chill the butter in the freezer for 10 minutes.
Mix together the flour, cornstarch, baking soda, and salt together in a small bowl and set aside.
Beat the butter and both sugars until light and fluffy.
Add in the egg, yolk, cream, and vanilla.
Stir in the flour mixture and mix.
Fold in the chocolate.
Preheat oven to 350F.
Bake for 10 minutes.
