Heat oven to 425°. Pulse flour, 6 tbsp. butter, and 1⁄2 tsp. salt in a food processor into pea-size crumbles. Add 1⁄4 cup ice-cold water; pulse into a dough. Form into a disk; wrap in plastic wrap; chill for 1 hour. Roll dough 1⁄8" thick on a floured surface. Transfer to a 9" pie plate, trim edges, prick with a fork. Cover with parchment; fill with dried beans. Bake for 20 minutes. Remove paper and beans; bake until golden brown, 10-12 minutes. Let cool.
Whisk together cream, sugar, and 1 tsp. vanilla to stiff peaks; set aside. Place peanut butter and chocolate in separate bowls. In a 4-qt. saucepan, whisk together remaining salt, brown sugar, cornstarch, yolks, and milk. Bring to a simmer over medium heat; cook until custard thickens, 2-3 minutes. Remove from heat; whisk in remaining butter and vanilla. Strain through a sieve, and divide custard evenly between peanut butter and chocolate; whisk each until smooth. Fold half the whipped cream into the peanut butter, and spread evenly in pie crust; chill 20 minutes. Spread chocolate over top; chill until set, at least 45 minutes. Spread remaining whipped cream over pie.