Right, this is a German recipe so it's for 28 cm diameter springform, you can put it into a slightly smaller one too:
100 g butter
100 g sugar
some vanilla essence
3 egg yolks
150 g flour
55 g starch , any type will be fine
1.5 tsp baking powder
Cream butter and sugar, add egg yolks, add flour, starch and baking powder, put into the bottom of a baking paper lined springform. This isn't a soft batter, I press it into the baking tray with my hands. It will be nice and fluffy once baked nevertheless.
Arrange a layer of peeled rhubarb on top. Works well with other tart fruit too, gooseberries for example.
3 egg whites
pinch of salt
150 g sugar (my mum always used half caster and half icing, not sure why, it works with either one)
Beat egg whites with salt until stiff, carefully add sugar, pile the meringue mix on top of the rhubarb.
Bake at 160 C for at least 80 min, you can prop the door slightly open for the last 20 min to let any steam escape so that the meringue can crisp up.
Best eaten fresh.