Line 2 (1 1/2-quart) bowls with aluminum foil. Spoon ice cream evenly into bowls; smooth top with back of spoon. Sprinkle each with pumpkin pie spice. Cover and freeze 8 hours or overnight.
Beat whipping cream until foamy; gradually add powdered sugar, beating until soft peaks form. Stir in vanilla and food coloring.
Remove ice cream from bowls, and remove foil. Place ice-cream halves together to resemble a ball, and place on a serving plate. Spread with tinted whipped cream to resemble a pumpkin. Place citron on top to resemble a stem. Store in freezer until ready to serve. Serve with chocolate sauce, if desired.