Grease a 9x15 pyrex dish. Cover bottom with wax paper.
Put peanut butter and butter in a large microwavable bowl. Do Not Cover! I used a large glass casserole dish and that seemed to work perfectly. Microwave on high for 2 minutes.
Remove from microwave. Stir to combine. Return to microwave for another 2 minutes on high.
Remove from microwave. Add the vanilla extract to the mixture and stir to combine. Add the powdered sugar and stir combine. You are done stirring once the mixture appears evenly combined.
Pour the mixture into the prepared dish. Use a second sheet of wax paper to cover the fudge and smooth the top. Place in the fridge to cool. Once cool, discard the wax paper cover and cut into pieces and serve.