Roll 1 piecrust to press out fold lines; cut out leaves with a leaf-shaped cutter. Brush leaves with lightly beaten egg, and place on a baking sheet; set aside.
Fit remaining piecrust into a 9-inch pieplate according to package directions; fold edges under and crimp.
Bake leaves at 350° for 10 to 12 minutes or until golden. Bake piecrust for 6 minutes or until lightly browned. Remove leaves and piecrust from oven; let cool. Increase oven temperature to 425°.
Combine 1/2 cup light brown sugar, chopped walnuts, butter, and vanilla extract; spread on the bottom of baked piecrust.
Beat pumpkin, cream cheese, 2 eggs, and remaining 3/4 cup brown sugar at medium speed with an electric mixer. Add flour, cinnamon, ginger, allspice, and nutmeg, beating until blended. Spoon pumpkin mixture over walnut mixture.
Bake at 425° for 15 minutes. Reduce temperature to 350°, and bake 30 more minutes or until pie is set. Remove pie to a wire rack; cool. Arrange leaves on top of pie. Serve warm or chilled with whipped cream, if desired.