1. Beat egg whites and ½ cup sugar until stiff peaks form.
2. Beat yolks with 1 tablespoon sugar, oil, vanilla sugar, if using, and potato starch. Combine lemon juice, remaining sugar, and fruit in mixing bowl.
3. Divide half of batter between 15 muffin tins. Spoon fruit mixture atop. Pour remaining batter over fruit.
4. Bake at 350°F for 45 minutes or until tops of muffins turn golden brown.