Beat butter, brown sugar and sugar with a paddle attachment until creamy.
Add in egg, yolk, vanilla.
Add soda, cornstarch, salt and flour.
Carefully add chocolate chips.
Chill dough 2 hours.
Preheat oven to 425.
Line cookie sheets with parchment.
Scoop out dough in large tablespoons.
Place in oven and immediately lower temp to 375.
Bake 6-8 minutes.
Remove and sprinkle extra chips on cookies.
Sprinkle on salt if desired.
Cool on sheets.