Note: Carrageen is a purple-brown or green fronded seaweed common on Scottish beaches on the mid-tide line. It can be used to set and delicately flavour a jelly or thicken a soup. If you gather your own fresh, you will need about 2 oz to set a pint of milk. Dried carrageen is available in health-food stores, or Chinese supermarkets in processed form, as agar-agar. *Rhubarb sticks should be sliced and lightly poached with additional sugar. Bring the milk to the boil with the lemon rind. Stir in the carrageen and cook for a couple of minutes until the milk thickens enough to coat the back of a wooden spoon. Add sugar. Allow the mixture to cool until it is at blood temperature (100 F, 40 C). Whisk the egg till frothy and then whisk in the warm milk until smooth. Pour the mixture through a sieve into a cold-wetted ring-mould. Then put it in the fridge to set it will only take about half hour. Run hot water over the outside of the mould and turn out the jelly. Fill the middle of the ring with a ladleful of rhubarb compote and surround with a little scarlet sauce of rosehip or redcurrant jelly melted in a little hot water.