Preheat the oven to 400 degrees F. Generously butter an oval baking dish or skillet that is attractive enough to serve from. Sprinkle with sugar. In a medium-size mixing 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, use an electric mixer to 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-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.
Using the rubber spatula, make three mounds of the mixture in the dish. Bake the souffle 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.