Instructions

 Roll dough into 12-inch circle on floured counter. Loosely roll dough around rolling pin and gently unroll it onto 9-inch pie plate, letting excess dough hang over edge. Ease dough into plate by gently lifting edge of dough with your hand while pressing into plate bottom with your other hand.
 Trim overhang to ½ inch beyond lip of plate. Tuck overhang under itself; folded edge should be flush with edge of plate. Crimp dough evenly around edge of plate. Wrap dough-lined plate loosely in plastic wrap and refrigerate until firm, about 30 minutes. Adjust oven rack to middle position and heat oven to 350 degrees.
 Line chilled pie shell with double layer of aluminum foil, covering edges to prevent burning, and fill with pie weights. Bake on foil-lined rimmed baking sheet until edges are set and just beginning to turn golden, 25 to 30 minutes, rotating sheet halfway through baking. Remove foil and weights, rotate sheet, and continue to bake crust until golden brown and crisp, 10 to 15 minutes longer. Transfer sheet to wire rack and let cool completely, about 45 minutes.
 For the Peanut Butter Mousse: Using stand mixer fitted with whisk attachment, whip sugar, peanut butter, cream cheese, and 2 tablespoons cream on low speed until combined, about 1 minute. Increase speed to medium-high and whip until fluffy, about 1 minute. Transfer to large bowl; set aside.
 In now-empty mixer bowl, whip remaining ½ cup cream on medium-low speed until foamy, about 1 minute. Increase speed to high and whip until stiff peaks form, 1 to 3 minutes. Gently fold whipped cream into peanut butter mixture in 2 additions until no white streaks remain. Spoon filling into cooled crust and spread into even layer with spatula. Refrigerate until set, about 1 hour.
 For the Grape Filling: While mousse chills, whisk ¼ cup sugar and pectin together in bowl; set aside. Bring grapes to simmer in large saucepan over high heat. Off heat, coarsely mash grapes with potato masher. Return to simmer over medium-high heat and cook until grapes have softened and pulp has separated from skins, about 5 minutes.
 Working in batches, strain grapes through fine-mesh strainer into large bowl, pressing firmly on solids to extract as much liquid as possible (you should have about 1¼ cups); discard solids. Return strained grape juice to now-empty saucepan. Bring grape juice, remaining ¾ cup sugar, lemon zest and juice, and salt to boil over medium-high heat. Whisk in pectin mixture, return to boil, and cook for 1 minute, whisking constantly. Let cool off heat until just warm, about 30 minutes. Slowly pour filling over peanut butter mousse, spreading into even layer with rubber spatula. Refrigerate until filling is set, about 2 hours. Spread whipped cream attractively over pie and sprinkle with candied nuts. Serve.