Twix Bar Chocolate Chip Cookies

unsalted butter, softened

light brown sugar, packed

granulated sugar

large egg

vanilla extract

all-purpose flour

cornstarch

baking soda

salt, optional and to taste

Twix, diced small and loosely piled in measuring cup (I used 26 mini size (not Fun Size) Twix from an 11.5-ounce bag; each bar diced into 4 small pieces)

semi-sweet chocolate chips