Pour 2/3 cup of the water into a small bowl, sprinkle in the gelatine and set the bowl aside for 10 minutes, or until the gelatine is swollen and opaque.
Meanwhile, scald a large saucepan and a balloon whisk with boiling water. Line a large nylon sieve with a double thickness of muslin or a clean tea towel, place over a large bowl and scald to remove all traces of grease.
Put the remaining water in the saucepan, add the gelatine and all the remaining ingredients. Whisk over medium heat until the mixture forms a thick, heavy, white froth on the surface.
Stop whisking, increase the heat and allow the froth to rise almost to the top of the pan, then immediately remove from the heat and allow the froth to settle back down. Repeat twice more and leave to stand for 5 minutes.
Taking care not to break up the froth, pour the jelly through the muslin-lined sieve into a 5-cup wetted jelly mould and refrigerate for 3–4 hours, or overnight, until ﬁrmly set.
To turn the jelly out, dip the mould up to the rim in very hot water for 5 seconds. Put a ﬂat plate on top of the mould and, holding both together tightly, invert and give a good, sharp shake to free the jelly. Remove the mould. If the jelly does not come out of the mould the ﬁrst time, dip briefly in hot water again and repeat the process.