01 - Line an 8x8-inch baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a medium saucepan over low heat, combine chocolate chips, sweetened condensed milk, and 2 tablespoons butter. Stir constantly until melted and smooth, then remove from heat and stir in vanilla extract.
03 - In a separate bowl, combine peanut butter, melted butter, and powdered sugar until smooth.
04 - Pour the chocolate mixture evenly into the prepared pan.
05 - Drop spoonfuls of the peanut butter mixture over the chocolate layer, then gently swirl using a knife or skewer to create a marbled effect.
06 - Tap the pan lightly on the countertop to eliminate any air bubbles.
07 - Refrigerate for at least 2 hours until completely firm.
08 - Lift the fudge from the pan using the parchment overhang, cut into 36 squares and serve chilled or at room temperature.