Fit piecrust into a 9-inch pieplate according to package directions; fold edges under, and crimp.
Cook milk in a medium-size heavy saucepan over medium-high heat, stirring constantly, 10 minutes or until thickened and bubbly. Remove from heat; stir in pumpkin.
Stir in 1 cup whipping cream and next 4 ingredients until smooth. Pour into crust.
Bake at 350° on bottom oven rack for 40 minutes. Cool completely on a wire rack. Chill 8 hours.
Cook 3 tablespoons water, corn syrup, and sugar in a small saucepan over medium heat, without stirring, until a candy thermometer registers 300° (hard-crack stage). Pour immediately over pie, and quickly spread mixture with a metal spatula. Let stand 2 hours before serving. Tap hard sugar topping with back of a spoon to crack.
Beat remaining 1 cup whipping cream at medium speed with an electric mixer until soft peaks form. Serve with pie.