Line a small 4x6-inch or 5x5-inch dish with foil, leaving an overhang on the sides to lift the fudge out easily.
In a 2-quart saucepan, melt the butter over medium-low heat.
Stir in the peanut butter and mix until smooth and well combined.
Remove the pan from the heat and stir in the vanilla extract.
Add the sifted powdered sugar and stir until the mixture is smooth.
Pour the fudge mixture into the prepared dish and smooth the top with the back of a spoon or a rubber spatula.
Cover the dish tightly and refrigerate for at least 1 hour or until the fudge is firm.
Once firm, lift the fudge out of the dish using the foil overhang, then cut it into pieces and enjoy!
