Roll 1 piecrust into a 12-inch circle on a floured surface. Fit into an 11-inch tart pan with removable bottom. Prick bottom and sides of pastry shell. Bake at 375° for 5 minutes. Let cool in pan on a wire rack. Sprinkle with chopped hazelnuts.
Beat eggs at high speed of an electric mixer. Add pumpkin and next 9 ingredients; beat well. Pour into pastry. Bake at 375° for 35 minutes. Cool in pan on wire rack. Cover and chill at least 2 hours.
Cut 30 shapes from remaining piecrust using a small leaf cookie cutter. Place on an ungreased baking sheet. Bake at 450° for 6 minutes. Remove to a wire rack; let cool.
Beat whipping cream until foamy; gradually add powdered sugar, beating until soft peaks form. Fold in crystallized ginger. Cover and chill 1 hour.
Arrange whole hazelnuts and pastry leaves on tart. Serve with whipped cream mixture.