Preheat oven to 350 degrees F. (180 C) Line a 13×9 inch pan with non-stick foil or parchment paper.In a medium-sized microwave-safe bowl, melt the butter on high. When butter is melted, stir in the sugar. Return the mixture to the microwave and heat until mixture is very hot but not bubbling (1 minute). Stir well to help dissolve some of the sugar – mixture should appear shiny.Stir in the cocoa, salt, baking powder and vanilla.
Add the eggs, beating till smooth; then add the flour and chips, stirring until combined. Spoon 3/4 of the batter into the prepared pan.Prepare peanut butter mixture by beating “Peanut Butter
Mixture” ingredients in a bowl until smooth. Drop spoonfuls of peanut butter mixture over brownie batter, then drop remaining brownie batter of peanut butter mixture – not covering it entirely but creating kind of a big speckled pattern. Gently drag a knife through top to create a pretty marbled effect.
Bake the brownies for 28 minutes, until a cake tester inserted into the center comes out dry.
Remove them from the oven and after 5 minutes, loosen the edges with a table knife. This helps prevent sinking as they cool. Cool completely (and chill for better cutting) then cut and serve.Makes 12 large or 24 normal size brownies
