1 lb fresh rhubarb
Juice and rind of one orange
Sugar to taste
1 sachet gelatine
Whipping cream, or: yogurt, fromage frais, evaporated milk,
whatever.
Stew the rhubarb with the orange rind/juice, sugar, and as little water as you can get away with. Melt in the gelatine (if you are vegetarian or vegan, use another gelling agent), and then put through food processor to make puree. Add the cream or substitute - I would use fromage frais, but yogurt is fine, or you might like whisked evaporated milk, if you like the taste. Then refrigerate until set.
If, like me, the mere thought of rhubarb sets your teeth on edge (it's one of the very few things I really can't eat!), then use a different fruit - gooseberries, perhaps, or dried apricots. Gooseberries are nicest if stewed with elderflowers, if you can get them, and dried apricots don't need any help. I've not quoted quantities for the sugar, because it depends on your taste.