Chocolate Chip Cookie Brownie Bars

or 170g) unsalted butter, softened to room temperature

packed light or dark brown sugar

granulated sugar

large egg, at room temperature

pure vanilla extract

all-purpose flour (spoon & leveled)

cornstarch

baking soda

salt

and 1/2 cups (270g) semi-sweet chocolate chips

unwrapped miniature peanut butter cups (or 2 cups chopped peanut butter cups)

(1 stick; 115g) unsalted butter

(226g) semi-sweet chocolate bars, coarsely chopped*

granulated sugar

large eggs, at room temperature

and 1/2 teaspoons pure vanilla extract

all-purpose flour (spoon & leveled)

salt