01 - Line an 8-inch square baking pan with parchment paper, allowing excess paper to hang over the sides for easy removal later.
02 - Combine chocolate chips, sweetened condensed milk, and butter in a heatproof bowl. Melt using a double boiler or microwave in 30-second intervals, stirring frequently until completely smooth and glossy.
03 - Pour the melted chocolate mixture into the prepared pan. Spread evenly with a spatula to create a uniform layer. Refrigerate for 30 minutes until firm to the touch.
04 - In a medium saucepan over low heat, combine peanut butter and butter. Stir constantly until melted and well blended. Remove from heat and whisk in powdered sugar and vanilla extract until smooth and creamy.
05 - Pour the peanut butter mixture over the chilled chocolate layer. Use a spatula to spread evenly, covering the entire surface. Return to refrigerator.
06 - Refrigerate for at least 2 hours or until completely firm throughout. The fudge should hold its shape when touched.
07 - Lift the fudge from the pan using the parchment paper overhang. Cut into 16 equal squares. Store in an airtight container in the refrigerator.