Prepare the pan: Line an 8x8 inch baking pan with parchment paper, leaving some overhang for easy removal.
Melt chocolate: In a heat-proof bowl, combine the chocolate chips and half of the sweetened condensed milk. Microwave in 30-second intervals until melted, stirring in between.
Mix peanut butter layer: In another bowl, combine the peanut butter, remaining sweetened condensed milk, powdered sugar, graham cracker crumbs, and vanilla extract. Mix until smooth.
Layer the fudge: Pour half of the chocolate mixture into the prepared pan, followed by all the peanut butter mixture, and then top with the remaining chocolate mixture.
Chill: Refrigerate for at least two hours until firm.
Slice and serve: Once set, lift the fudge from the pan using the parchment overhang and cut into squares.