Grease cookie sheet, cream butter and peanut butter. Add sugars, eggs, and vanilla. Add dry ingredients. Press into large cookie sheet. Bake 350 degrees for 15-18 minutes. Frost with extra peanut butter while still warm. When cool, frost with chocolate frosting or use homemade fudge frosting.
In a heavy 2 quart sauce pan, combine milk, butter and sugar. Over medium heat stir constantly with a wooden spoon until mixture comes to a boil. Boil 3 minutes. Remove from heat. Stir in marshmallows, chocolate chips, and vanilla. Stir until melted. Starting in a corner pour back and forth from corner to corner over the peanut butter bars when fudge is still warm and it will give you the smooth shiny look. Cool (over night is best for cutting through fudge topping, if you can wait that long...yum).