TO MAKE SAUCE: Ina medium sized saucepan, combine rhubarb and sugar.
Bring to a simmer over medium low heat.
Cook until the rhubarb is tender and translucent.
With a slotted spoon, transfer about 1 cup of the rhubarb to a small bowl and reserve for the waffle batter.
Boil the remaining rhubarb in syrup over medium heat, stirring occasionally, until slightly thickened, about 5 minutes.
(The sauce can be prepared ahead and stored, covered, in the refrigerator for up to 4 days. Bring to room temperature or heat before serving.) TO MAKE WAFFLES: In large bowl, whisk egg whites until frothy.
Whisk in milk and oil.
Stir in the reserved 1 cup cooked rhubarb.
Sift flours, sugar, baking powder and salt into a medium sized bowl.
Gently stir the dry ingredients into the egg milk mixture just until moistened.
Preheat a waffle iron to medium high.
(If your waffle iron is not nonstick, brush it lightly with oil.) Fill the iron about two thirds full.
Close and cook the waffles until they are nicely browned, about 4 minutes.
Repeat with the remaining batter, coating the waffle iron lightly with oil, if necessary, before cooking each batch.
Serve hot, topped with the rhubarb sauce.
NOTE: If you buy egg whites in a carton, use 2 Tablespoons of egg whites for one egg"white".