In a large bowl, combine the dry ingredients. Add the milk, club soda, egg yolk, lemon zest, vanilla, and oil, and beat well. In a separate bowl, beat the egg whites on high speed until stiff peaks form. Carefully fold the egg whites into the batter. Lightly spray or wipe a large regular or nonstick skillet with vegetable oil. Place the skillet over medium-high heat; drop the batter into the pan by tablespoonfuls to form 5 cm pancakes, and cook until they are golden brown on both sides. Per pancake: Cal. 39, Carb 6g, Protein 1g, Chol. 11mg, Fat 1g/28% Variations: Omit the lemon zest and add one of the following to the batter: 2 tablespoons minced lime zest 1.5 cups fresh raspberries 1.5 cups fresh blueberries Seeds from 1 vanilla bean *