Preheat the oven to 350 degrees.

Spray and 8 x 8 baking dish with cooking spray and set aside.

In a large bowl combine the butter, peanut butter, brown sugar, egg, vanilla, and flour. Mix until well combined.

Fold in the chocolate chips. Spread in the prepared pan.

Spoon the chocolate spread onto the top in three long, skinny rows.

Using a knife swirl the chocolate into the peanut butter batter. Bake for 20-25 minutes.

Remove from oven and cool completely. Cut and serve once cooled.