Preheat your oven to 350 degrees. Spray a 9 by 13 inch pan with cooking spray.

In a large bowl, stir the peanut butter, sugars, and egg together. Press it into the bottom of the pan. It will be a thin layer. (Dorothy suggests using cooking spray on your hands to make for easy spreading of this layer.)

Melt the chocolate and the butter together in a large microwave safe bowl in 30 second intervals, stirring between each one, until it is one smooth mixture.

Stir the eggs, sugar, and vanilla into the chocolate butter mixture until smooth. Then gently stir in to the flour.

Pour the batter over the peanut butter layer and bake for 32 to 38 minutes or until the edges are slightly cracked. Let it cool in the pan completely before cutting and serving.