750g rhubarb, tough peel removed and cut into smallish pieces
Combine in a bowl and allow to soak overnight.
Step 2 - next day:
for the short crust:
250g plain flour (it works very well with a combination of wholemeal and plain white)
125g butter (cold-ish)
1 tsp vanillasugar or 1/2 tsp vanilla essence
Combine everything and knead into a firm dough. If it is too sticky, put it in the fridge for a little while.
Roll out to line a 28/30 cm diameter spring form cake tin (greased, or lined with baking parchment), also lining the sides of the tin.
Now put the rhubarb, which by now will be swimming in some nice sugary rhubarb juice, into a colander and catch that juice. Keep the rhubarb aside.
Preheat oven to 175 degrees.
Pour the juice into a pan and add a packet of vanilla pudding powder (if living in Germany) or simply add 2 heaped tablespoons of cornflour (if living everywhere else). Bring to a boil while whisking continuously. Take off the heat and watch it thicken.
Put the rhubarb onto the crust, pour the thickened juice over.
Bake this at 175 degrees for about 25 minutes.
Meanwhile, prepare the topping - Step 3:
3 egg whites - beat until very stiff
3 egg yolks beaten separately with
2 tbsp lukewarm water
1 pot of soured cream or creme fraiche - fold this into the egg yolk mix, then carefully fold in beaten egg whites.
Distribute this topping on the rhubarb, then bake for another 25 minutes, or until golden brown.