From my friend, Danielle
2 cups flour
1/2 teaspoon kosher salt
1/2 teaspoon baking soda
1 1/2 sticks softened butter
1 cup brown sugar
1/2 cup sugar
1 tablespoon vanilla
1 egg yolk
1 cup semisweet chocolate chips
1 cup bittersweet chocolate chips
Preheat oven to 350º. Line cookie sheets with parchment.
Cream butter and sugars till well blended. Add vanilla, eggs and egg yolk, and mix till light and creamy. Stir in flour, salt and baking soda till just incorporated. Stir in chocolate chips. Chilling dough is optional.
Drop by 1/4 cups onto baking sheets. Bake about 14-16 minutes till edges are browned and centers look cooked. Cool on sheets.