1. To prepare sauce, combine 1/4 cup water, juice, and 1 tablespoon sugar in a small saucepan; bring to a boil. Cover, reduce heat, and cook until reduced to 2/3 cup (about 6 minutes). Combine cornstarch and remaining 1 teaspoon water in a small bowl, stirring with a whisk. Stir into juice mixture. Bring to a boil; cook for 1 minute or until slightly thickened, stirring constantly. Remove from heat; stir in butter and 1/2 teaspoon orange rind. Keep warm.
2. To prepare pancakes, weigh or lightly spoon flours into dry measuring cups; level with a knife. Combine flours, baking powder, baking soda, and salt in a large bowl; stir with a whisk. Combine buttermilk and next 3 ingredients (through egg yolk) in a small bowl, stirring with a whisk. Add the milk mixture to flour mixture, stirring with a whisk (batter will be thick). Place egg whites in a large bowl; beat with a mixer at high speed until soft peaks form. Add 2 tablespoons sugar, 1 tablespoon at a time, beating until stiff peaks form. Gently stir one-fourth of egg white mixture into batter. Gently fold in the remaining egg white mixture. Gently stir in sparkling water.
3. Pour about 1/4 cup batter per pancake onto a hot nonstick griddle or nonstick skillet, and spread gently with a spatula. Cook for 2 minutes or until tops are covered with bubbles and edges look cooked. Carefully turn pancakes over; cook 2 minutes or until bottoms are lightly browned. Top with bananas. Serve with sauce.