Soak top and bottom of a clay pot in water for at least 15 minutes. To prepare batter, combine cake mix, dry lemon gelatin, vanilla extract, egg whites, water, and oil in a mixing bowl. Line bottom and up sides of pot with waxed paper. Cover, and place in a cold oven. Set temperature to 400 degrees. Bake for 45 minutes or until springs back when touched.
Meanwhile to prepare topping, combine fruit juice, powdered sugar, lemon juice, and water in a saucepan. Stir over medium heat until sugar has dissolved. Remove cake from oven. Prick top all over with a fork and immediatley pour fruit juice mixture over top.