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 ½ hour.
Run hot water over the outside of the mould and turn out the jelly.
Fill the middle of the ring with a ladelful of rhubarb compote and surround with a little scarlet sauce of rosehip or redcurrant jelly melted in a little hot water.