The first 6 ingredients are what the cake batter is made of.
Fold rhubarb into batter.
Mix topping together then sprinkle over top of batter then--
Pour carefully over the top of it 1 cup of boiling water.
(if it looks like the 1 cup of water is going to overflow a pan then just use enough to not overflow the pan or baking dish - it's a real mess in your oven if it does drip over .
use tin foil on the bottom of a baking sheet to prevent spills).
Bake for approx. 45-50 minutes at 375 degrees (a little longer if you double the recipe for a larger baking dish).