1Prepare an 8x8-inch baking pan by lining it with aluminum foil and spraying the foil with nonstick cooking spray.
In a medium saucepan, melt the butter. Once it is completely melted, stir in the brown sugar and the milk.
Boil the mixture for 2 minutes, stirring frequently. After 2 minutes, remove from the heat and stir in the peanut butter and vanilla.
Sift the powdered sugar into a large bowl, and pour the peanut butter mixture over the sugar. Stir until the candy is well-combined and has no lumps.
Pour the fudge into the prepared pan. Cover the pan with cling wrap, and refrigerate until firm. Once firm, cut into small squares to serve.