Step 1

Preheat oven to 350F. Line an 8-by-8-inch baking pan with aluminum foil, spray with cooking spray; set aside.

Step 2

To a large, microwave-safe bowl add the butter and heat on high power to melt, about 1 minute.

Step 3

Wait momentarily before adding the egg so you don’t scramble it. Add the peanut butter, egg, brown sugar, vanilla, and whisk until smooth.

Step 4

Add the flour and stir until just combined, don’t overmix.

Step 5

Add 1/2 cup chocolate chips and stir to combine.

Step 6

Turn batter out into prepared pan, smoothing the top lightly with a spatula.

Step 7

Evenly distribute the peanut butter cups over the surface of the batter, pushing each cup down as far as it will go.

Step 8

Evenly sprinkle the surface with additional chocolate chips, about 1 tablespoon.

Step 9

Bake for about 22 to 25 minutes, or until done. If you can find a chocolate chip-free patch to test, a toothpick inserted in the center should come out clean, or with a few moist crumbs, but no batter.

Step 10

Allow bars to cool in pan for at least 1 hour before slicing and serving.