Step 1

In a medium-sized, microwave-safe bowl, combine the butter, sugar, and milk. Cover with a paper towel or plastic wrap and microwave for 2 minutes. Stir, then, microwave for 2 more minutes.

Step 2

Carefully remove the bowl from the microwave and add the peanut butter, marshmallow fluff, and vanilla extract, and stir to combine.

Step 3

Sift in the powdered sugar, stir, and let chill until hardened, about 4 hours.