Cream butter and peanut butter; gradually add sugar, beating until light and fluffy.
Stir in vanilla.
Add the eggs, one at a time,.
beating well after each.
Combine flour, baking powder, and salt; add to creamed mixture alternately with milk, beginning and ending with flour mixture.
Grease bottom (not sides) of two 9-inch microwave-safe cakepans, and line with waxed paper; grease waxed paper.
Spoon batter into pans.
Cut through batter with a knife to remove the air bubbles.
Place 1 pan in microwave oven or an inverted saucer.
Microwave at MEDIUM (50% power) for 5 to 6 minutes, giving pan a half-turn at 2-minute intervals and at end of cooking time.
Microwave at HIGH for 2 to 3 minutes or until top is almost dry.
Remove from oven and place on a sheet of aluminum foil.
Cool in pan 10 minutes; remove from pan, and cool on a wire rack.
Repeat with remaining layer.
Spread Chocolate Frosting between layers and on top and sides of.
Sprinkle peanuts over top.
Yield: one 2-layer cake.
CHOCOLATE FROSTING: Combine chocolate, butter, and milk in a large microwave-safe mixing bowl; microwave at MEDIUM (50% power) for 3-1/2 minutes or until mixture is softened and blended, stirring after 3 minutes.
Stir in remaining ingredients; let stand 10 minutes.
Beat with a wooden spoon until of spreading constistency.