Preheat oven to 350ºF.In a medium size bowl, break the egg yolks up with a fork and stir in the vanilla and lemon peel. Sprinkle the flour over the yolk mixture. In another bowl, using a wire whisk or rotary or electric beater, beat the egg whites with a pinch of salt until they cling to the beater. Add the sugar and beat until the whites form stiff, unwavering peaks. With a rubber spatula, stir an overflowing tablespoon of the whites into the yolk and flour mixture, then reverse the process and fold the yolk mixture into the rest of the egg whites, using an over-under cutting motion instead of a mixing motion. Don't over fold. Generously butter an oval or oblong 8x10x2 inch baking dish, attractive enough to serve from. Using the rubber spatula, make 3 mounds of the mixture in the dish. Bake the Nockerl in the middle of the oven 10 to 12 minutes, or until it is lightly brown on the outside but still soft on the inside. Sprinkle with confectioners' sugar and serve immediately. Serves 6.