Oldroyd's website for a fascinating history of this product.
Anyway, cut a pack, about 4 long, slender, shocking pink sticks, into chunks and put in a single layer if possible in a baking dish. Now, zest an orange, and stir into 3 tablespoons of caster sugar, and sprinkle over the rhubarb. Juice the orange and pour over the sugary chunks. Bake at 160C for 20-25 minutes until the rhubarb is tender and the whole thing is lovely and juicy. Allow to cool. Take out your ice cream from the freezer and allow to soften for 10 minutes. Now, either tip into a food processor with the cold cooked rhubarb and juices and blitz in short sharp buzzes until rippled through, or roughly blend the rhubarb until still a bit chunky, tip the ice cream into a bowl and fold the blended rhubarb through. Either way, Pour the ice cream into a lidded plastic container and return to the freezer sharpish so it can all settle and freeze again. Serve with more roasted rhubarb and some crisp little biscuits - shortbread, perhaps, or I like Bonne Maman Butter Galettes for a complete cheat's dessert!