Preheat the oven to 375°. In a food processor, pulse the cookies and butter until the cookies are finely ground. Transfer to a 10-inch tart pan with a removable bottom. Using a measuring cup or glass, press the crumbs onto the bottom and up the sides of the pan; freeze until firm, about 30 minutes. Place on a baking sheet; bake until firm, 12 to 15 minutes. If the crust puffs, press down with the measuring cup. Let cool on a wire rack.
To make the filling, place a metal bowl over a saucepan of barely boiling water. Add the peanut butter cups, peanut butter, cream, cream cheese and salt. Cook, stirring often, until melted. Pour into the crust. Top with Reese’s Pieces; chill until set, at least 2 hours.
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