Preheat oven to 350 degrees F. Line a 9x13 inch metal baking pan with foil and spray bottom with cooking spray. If halving the recipe, use an 8 inch square pan.

Melt butter in medium saucepan over low heat. Add 2 cups of the sugar (reserve the 2 tablespoons for later) and cocoa; stir to blend. Remove from heat. Stir in eggs and vanilla. Stir together flour, salt and baking soda and add to chocolate mixture.

At this point, make sure the batter is no longer warm so that it won't melt the add-ins. Stir in the peanut butter chips and about ½ cup of the mini peanut butter cups and spread evenly in the pan.

Mix only ½ cup of the peanut butter with the 2 tablespoons of reserved sugar and drop by tablespoons onto chocolate batter. Gently pull a knife through (just a bit) to marble.

Bake 25 to 30 minutes or until brownie starts to pull from edges of pan and is set. The peanut butter part that's showing should look a little dried out. This is normal.

Set on a wire rack. Immediately, while the brownies are still hot out of the oven, start spooning the remaining peanut butter (you don't have to use all of it) over the areas where the baked peanut butter shows. The point is to cover the baked peanut butter with the fresh peanut butter so that it melts over it and looks smooth. Top should still look very swirled. As you dollop with more peanut butter, sprinkle the remaining chips over the top (feel free to cut some in half) artfully.

Let cool completely, then chill just until chocolate and peanut butter are set. Lift from pan and cut into squares.