Preheat the oven to 350 degrees F. Grease a 9 by 13-inch glass baking dish.
Melt the butter over low heat; when melted remove from heat and stir in the sugar and vanilla. Add the eggs 1 at a time, beating after each addition. Add flour, cocoa, baking powder and salt, and mix well.
Mix the peanut butter and chocolate spread in a small microwave-proof bowl, and heat in the microwave until it reaches a runny consistency. Stir the mixture into the batter; then pour it into the baking dish. Bake for 30 minutes. Allow to cool before cutting and serving.
Recipe courtesy of Bethany Burchick from Pittsburgh, PA