Pam/Baker's Pride spray baking pan well. Pour into pan dry ingredients. Sprinkle over all the cut rhubarb, scattering evenly.
Drizzle all liquids to wet down dish contents, then draw knife through to distribute mingling wet & dry. Adjust amount of added liquid if needed, but don't expect it to be batter-like; cooking rhubarb will provide more juice!
Can be doubled for 9 X 13, but I'd only do a bit more than half again of the rhubarb.
Bake at 350 - 35 minutes (+or-) Check that bottom is cooked, cake-like, then cool, but serve warm with whipped cream/ icecream or drizzle with heavy cream/half-and-half.
Keep leftovers wrapped well to prevent drying out or freeze/thaw to enjoy later. (substitute other fruits/juices/jellos to vary)