What I tend to do with fruit like rhubarb, plums etc. is just cut into pieces and 'stew' until soft in a pan over a gentle heat in a little no added sugar squash (preferably not orange or lemon anything too citrussy, but apple and blackberry, forest fruits etc. any of those sorts of flavours work best ) or if not, a little bit of fresh apple juice - it bleeds its own juice as it cooks anyway, so only needs a tiny bit of liquid to get it started. Once it's cooled just store it in a tupperware container or jar in the fridge and just stir a couple of spoonfuls into natural yoghurt or fat free vanilla yoghurt as and when. Delicious.