Instructions

• Preheat the oven to 375°F.
• Put all 14 Oreo cookies in a food processor and process into fine crumbs. Melt the 4 tablespoons butter and add it to the cookie crumbs; process until evenly combined. Press the mixture into a 9-inch pie pan, covering the bottom and up the sides. Bake the crust for 8 minutes. When it comes out of the oven the crust may puff and shrink; use the flat bottom of a drinking glass to gently press it back into an even layer. Cool the crust completely.
• In the food processor, process 20 of the fun-size Butterfinger bars into fine crumbs. Divide those crumbs into three portions: two 1/2-cup portions and one 1-cup portion; set them aside. Chop the remaining 3 fun-size Butterfinger bars and set the chopped pieces aside for the topping.
• In a medium saucepan, whisk together 1/2 cup granulated sugar, 2 tablespoons cornstarch, and 2 cups whole milk until smooth. Cook over medium heat, stirring constantly, until the mixture comes to a gentle boil and begins to thicken.
• While the milk mixture is hot, beat the 2 large egg yolks in a small bowl. Whisk about 1 tablespoon of the hot milk mixture into the yolks at a time until the yolks are warmed and tempered. Pour the tempered yolks back into the saucepan with the remaining milk mixture and return to medium heat. Stir constantly and cook until the mixture thickens to a pudding-like consistency (bring to a brief boil while stirring). Remove from heat.
• Whisk 1/2 cup creamy peanut butter into the hot custard until smooth. Scoop out 1 cup of this peanut butter mixture into a medium bowl and set that bowl aside to cool completely (this will become the peanut butter mousse layer).
• To the remaining peanut butter mixture in the saucepan, add 1/2 cup milk chocolate chips and one of the reserved 1/2-cup Butterfinger-crumb portions. Stir until the chocolate chips are fully melted and the mixture is smooth. Pour this chocolate-Butterfinger mixture into the cooled Oreo crust and spread evenly. Refrigerate the pie while you prepare the next layer so the chocolate layer can set slightly.
• Use an electric mixer to whip 1½ cups whipping cream to stiff peaks. Fold the whipped cream into the cooled 1 cup peanut butter mixture (from step 6) until smooth, then fold in the other reserved 1/2-cup Butterfinger-crumb portion.
• Remove the pie from the refrigerator and spread (or mound) the peanut butter-whipped cream mixture evenly over the chilled chocolate layer, smoothing to the edges.
• Whip 2 cups heavy whipping cream to stiff peaks. Fold in the reserved 1-cup Butterfinger-crumb portion. Spoon this whipped cream mixture over the top of the pie, mounding slightly in the center.
• Sprinkle the chopped 3 fun-size Butterfinger pieces over the top of the pie. Cover loosely and refrigerate until ready to serve.