Another recipe pilfered from food network.
1 cup butter, plus more for greasing pan
1 cup peanut butter
1 teaspoon vanilla
2 1/2 cups powdered sugar
Microwave butter and peanut butter for 2 minutes on high. Stir and microwave on high for 2 more minutes. Add vanilla and powdered sugar to peanut butter mixture and stir to combine with a wooden spoon. Pour into a buttered 8 by 8-inch pan lined with waxed paper. Place a second piece of waxed paper on the surface of the fudge and refrigerate until cool. Cut into 1-inch pieces and store in an airtight container for up to a week.
It doesn't say to, but I would recommend sifting the powdered sugar to get rid of the clumps. Mine didn't break apart well when mixing this up and i had some lumps.