Line the bottom and sides of an 8x8x2 inch pan with aluminum foil or wax paper. Butter the foil or wax paper. Place the peanut butter, butter and salt in a large microwaveable bowl and cook in the microwave for two minutes on high. Stir and continue to microwave (if needed) until the ingredients are completely melted. Stir in the vanilla extract and confectioners sugar. Spread the fudge into the prepared pan, smoothing the top with an offset spatula or spoon. Cover and place in the refrigerator until cool. To serve, cut into 1” pieces. Can be stored in the refrigerator for up to one week. Makes about 64 – one inch pieces of fudge