Mix together the first 4 ingredients and put into a 2 quart baking dish.
To prepare the topping: Mix dry topping ingredients together. Beat 1 large egg until frothy. Add to the dry mixture.
If the topping mixture seems a little too dry, add one tablespoon of water to the topping, then crumble over the rhubarb. Crumble topping over the top of the rhubarb. Bake at 350 degrees for 40 minutes. Serve warm with whipped cream or ice cream.