Preheat oven to 350. Combine confectioners' sugar and peanut butter in small bowl. Sprinkle half of peanut butter mixture on bottom of pastry shell. Stir together sugar, cornstarch, flour, and salt in medium saucepan; gradually stir in milk. Bring to a boil over medium heat, stirring constantly. Reduce heat to medium-low and cook for an additional 2 minutes, stirring constantly. Remove pan from heat. Gradually stir one cup hot mixture into egg yolks; return egg mixture to saucepan. Return mixture to a boil over medium-low heat and cook for 2 minutes, stirring constantly. Remove pan from heat; stir in butter and vanilla. Pour filling over peanut butter mixture in pastry shell. Spread meringue on hot filling. Carefully sealing to edge of crust to prevent shrinking. Sprinkle remaining peanut butter mixture over meringue. Bake for 12 to 15 minutes or until light golden brown. Cool completely on wire rack before serving or refrigerating.