in a large mixing bowl add melted butter and sugar and vanilla, mix well.
add eggs one at a time, mix well after each egg.
add flour, cocoa, baking powder and salt, beat until well blended.
with a spoon stir in nuts and chocolate chips. pour into pan, spread evenly.
in 3 small microwavable bowls warm the peanut butter in one the nutella in one and the carmel sauce in one, drizzle each over brownie mix, drag a knife through it and swirl it around back and forth across the pan, to marblize it.
Bake for about 30 minutes or until brownie starts to pull away from sides of pan. Cool completely, (if you can) and enjoy. Extra special with a dallop of whipped cream and a cherry on top or some vanilla cool whip frosting or some ice cream