There are 3 traditional English cream desserts, trifle,fool & syllabub. Syllabub is sweetened cream whipped with fruit juice, zest & alcohol. Fool is unsweetened cream combined with fruit compote. Of the two I have a ridiculous attachment to fool, preferably rhubarb or gooseberry. It's a bit early yet for gooseberries so ...
What you do now depends on a couple of things, if you have nice pink chunks of rhubarb, whip a few out to decorate your finished dish with. If its older green rhubarb cook it down to a compote. The pink stuff you can simmer till soft. Put the whole lot through a sieve to get some pinkish rhubarb juice/syrup, reserve that & then sweeten the rhubarb to taste (probably 50-100g of sugar). Let everything cool. If you like you can sneak some of the syrup away for cocktail making (more on this in a later post). Whilst all that is going on its time to whip 500ml of cream, use the good stuff and whip it to soft peaks.
Fold your syrup into the cream, if it won't all go give the cream an extra bit of whipping & carry on till its all in.
Its well worth making both a fool & a syllabub to compare the tastes & textures. It'll take a lot to convince me that the fool isn't superior though.