Melt butter in a large microwave-safe mixing bowl.
With a whisk or just a big spoon, beat both sugars into melted butter. Let cool for about 5 minutes, and then beat in vanilla, egg and egg yolk.
When mixture is well blended, beat in baking soda and salt, scraping sides of bowl to make sure baking soda is evenly distributed. Add flour and stir just until it is mixed in. Add chocolate chips. Chill dough for 1 hour or until pretty firm.
Preheat oven to 350 degrees F. Line baking sheets with parchment.
Scoop up tablespoonfuls of dough and drop 1 inch mounds (approx) onto cookie sheets spacing about 3 inches apart. Bake for 13-15 minutes or until cookies appear done and lightly browned around edges.
Cool on sheet for 5 minutes, then transfer to a rack to finish cooling
Makes 18-24, depending on how big you make your mounds and whether or not you add the extra chips