Preheat oven to 350°F. Sprinkle a little sugar over the piecrust and bake until it is light golden-brown (about 15 minutes) (poke it with a toothpick or fork if it bubbles during the baking process). Cut the lemon into chunks, leaving the rind on and removing the seeds. In a blender or food processor, blend together lemon chunks, eggs, butter, vanilla, and sugar until the mixture is smooth and creamy (it should be fairly runny). Pour the mixture into the pre-baked piecrust. Bake at 350°F for about 40 minutes. If the crust becomes too brown, cover it gently with foil and finish baking. Let it set up for about an hour, then refrigerate it to chill. Serve it with a dollop of fresh whipped cream.