I simmered rhubarb until it was the right consistency. Then strained through a sieve and allowed it to cool down. I then whisked 110g of icing sugar into 150ml of mascarpone. Then I folded that mixture into 150g of creme fraiche, before finally folding in the rhubarb. Then I poured the lot into a dish and chilled it.
It came out with the texture of a thick yoghurt - not quite what I was after.