01 - Line an 8x8-inch baking pan with parchment paper, ensuring an overhang on the sides for easy removal of the fudge.
02 - In a medium saucepan over low heat, combine chocolate chips, sweetened condensed milk, and 2 tablespoons of butter. Stir constantly until the mixture is melted and smooth. Remove from heat and stir in vanilla extract.
03 - In a separate bowl, mix creamy peanut butter, melted butter, and powdered sugar until smooth and creamy.
04 - Pour the chocolate mixture into the prepared pan and spread evenly.
05 - Drop spoonfuls of the peanut butter mixture over the chocolate layer. Use a knife or skewer to swirl gently to create a marbled pattern.
06 - Refrigerate for at least 2 hours, or until the fudge is firm.
07 - Lift the fudge out of the pan using the parchment paper overhang. Cut into 16 squares and serve.