Place the butter, brown sugar and granulated sugar in a large mixing bowl and beat on medium-high speed until very pale and fluffy (3 to 5 minutes).
Add the egg, egg yolk, and vanilla, beating until completely incorporated.
Scrape the bottom and sides of the bowl with a silicone spatula, then add the flour, cornstarch, baking soda, and salt, stirring on medium-low speed just until all the ingredients are combined (do not over-mix).
Stir in the chocolate chips.
Use a 1 1/2-tablespoon cookie scoop to drop balls of cookie dough onto the prepared sheets, allowing about two inches in between (for spreading).
Bake (one sheet at a time) on the center rack of the oven for 7 to 10 minutes, or until set around the edges and just barely beginning to turn golden.
Cool completely on the baking sheet, then transfer to an air-tight container for storage.
Soft Chocolate Chip Cookies
Amount Per Serving
Calories 176Calories from Fat 81
% Daily Value*
Saturated Fat 5g31%
Vitamin A 165IU3%
* Percent Daily Values are based on a 2000 calorie diet.