01 - Line an 8-inch square baking pan with parchment paper, ensuring an overhang for easy removal of the set fudge.
02 - In a medium saucepan over medium heat, combine and melt the butter and peanut butter, stirring continuously until a smooth, cohesive mixture forms (approximately 2-3 minutes).
03 - Remove the saucepan from the heat. Stir in the pure vanilla extract and fine sea salt until fully integrated into the mixture.
04 - Gradually introduce the sifted powdered sugar to the mixture, stirring until a smooth and very thick consistency is achieved. A wooden spoon or a hand mixer may be necessary to incorporate fully.
05 - Pour the fudge mixture into the prepared baking pan. Utilize a spatula to spread and smooth the top surface evenly.
06 - Immediately and uniformly sprinkle the flaky sea salt over the surface of the fudge, gently pressing it into the mixture to adhere.
07 - Refrigerate the fudge for a minimum of 2 hours, or until it has completely set and achieved a firm texture.
08 - Using the parchment paper overhang, carefully lift the set fudge from the pan. Cut into 36 uniform, small squares. Serve chilled or at room temperature.