01 - Line an 8-inch square baking pan with parchment paper, allowing some overhang for easy removal.
02 - In a medium saucepan over low heat, combine chocolate chips, sweetened condensed milk, and 1/4 cup butter. Stir constantly until the mixture is melted and smooth. Remove from heat.
03 - Pour two-thirds of the chocolate mixture into the prepared pan and spread evenly. Reserve the remaining one-third for the top layer.
04 - In a medium bowl, combine creamy peanut butter, powdered sugar, melted butter, and vanilla extract. Mix until the mixture is smooth and creamy.
05 - Gently spread the peanut butter mixture over the chocolate layer in the pan.
06 - Reheat the reserved chocolate mixture slightly if needed, then carefully spread it over the peanut butter layer.
07 - Sprinkle chopped peanuts and flaky sea salt on top, if desired.
08 - Refrigerate the fudge for at least 2 hours, or until it is completely set.
09 - Lift the fudge out of the pan using the parchment paper, cut it into squares, and serve.