Line 13x9 inch pan with foil covering all sides.
To make Blondie Layer: Mix flour, cocoa, baking powder and salt. In another bowl beat butter, sugar and vanilla until creamy. Beat in egg, one at a time. On low, beat in flour mixture. Stir in peanuts. Spread into pan; level top.
To make Cheesecake Layer: Beat cream cheese until smooth. Add sugar, eggs and flour. Gently spoon over Blondie layer and carefully smooth over.
To make Brownie Layer: Stir in flour, cocoa, baking powder, and salt. In another bowl beat butter and sugar until creamy. Add eggs one at a time. Add peanut butter. On low speed add 1/2 the flour mixture then add 1/2 the milk. Repeat. Gently spoon over Blondie layer and carefully smooth over. Place a tent of aluminum foil over the top of the pan (make sure to "tent" the foil because otherwise the top brownie layer will stick to the foil and it wont look good).
Bake at 350°F covered for 1 hour, remove foil and bake 25-30 minutes longer. Place on rack to cool 30 minutes. Refrigerate at least 2 hours or up to 24 hours.
Garnish: Either prepare chocolate mousse mix according to directions using only 1 cup milk and spread on top or melt a jar of chocolate frosting for 30 seconds in the microwave and pour over the top (if you do this you'll want to refrigerate for an additional hour). Once on serving plate garnish with caramel topping, chocolate shavings and chopped peanuts. Yum!