Rhubarb: Try to work w/ slim red rhubarb stalks.
Flour: Adjust the amount of flour according to your preference - more or less cake!
Cornstarch: You may also use potato starch.
Ice cream is optional; you may also add some whipped cream or simply nothing!
You may also let it cool down to room temperature & serve then.
The dessert is fine for at least 2 days when sitting on your kitchen counter.
You may also store any leftovers in the fridge for at least 2 - 3 days.
Coming out of the fridge it might be useful to reheat the dessert in the microwave.
Sorry: no experience w/ freezing.