Preheat oven to 425 degrees. Line cookie sheets with parchment.
Beat butter and both sugars until well blended.
Add in vanilla, egg and yolk until light and creamy.
Add in flour, salt and baking soda just until incorporated.
Stir in both kinds of chocolate chips by hand.
Optional: Chill 4 hours.
Drop by 2 ounce mounds onto parchment.
Place in oven and IMMEDIATELY lower temp to 375. Bake 9 minutes or until tops golden.
Let cool on cookie sheets.
For the second batch, put the oven back up to 425 and repeat the directions.
MAKES 21 COOKIES (2 OUNCES EACH)