Fit the piecrust into 9 inch pie plate according to package instructions, fold the edges under and crimp them. Bake piecrust at 425 for 7 minutes or until it is lightly browned. Let piecrust cool. Combine nectar, whipping cream, egg yolks, sugar, cornstarch and salt in a medium saucepan. Bring to a boil over medium heat, whisking constantly. Boil for 1 minute or until it thickens, whisking constantly. Remove from heat. Stir in the butter and vanilla. Cover tightly with plastic wrap and cool to room temperature. Spoon mixture into prepared piecrust, cover and chill for 8 hours. Garnish with whipped cream and mango slices.