This dessert is baked using a technique called a "bain marie" (water bath), in which the baking dish is set inside a larger pan filled with hot water.From the book "Mad Hungry" by Lucinda Scala Quinn (Artisan Books).
Preheat the oven to 350 degrees Fahrenheit. Using the teaspoon of butter, butter six 2-ounce baking cups or one 12-ounce (8 x 10-inch) oval baking dish. Place the cups or dish in a roasting pan. Bring a tea kettle or medium pot of water to a boil.
Meanwhile, in a large bowl, beat the egg whites until stiff. In another clean bowl, beat the egg yolks until frothy and light in color, 3 to 4 minutes. Slowly add the sugar to the yolks while still beating. Mix in the lemon zest and juice.
Gently fold the egg whites into the egg yolk-lemon mixture. Pour the batter into each souffle cup (filling each three-quarters full) or the baking dish. Put the roasting pan on the oven rack with the oven door open. Carefully and quickly pour the boiling water into the roasting pan to come halfway up the sides of the baking cups or dish. Slide the pan into the oven and bake for 20 to 25 minutes. Don't overcook.
Remove the pan from the oven. Set the cups or dish on a wire rack to cool. To serve, set the cups on serving plates or scoop from the baking dish into individual dishes. Dust with confectioners' sugar, then top with a dollop of whipped cream.