I've often made this and it really is delicious.
Peel the fruit and discard the pulp.
Slice the peel as thinly as possible or dice.
Soak in water for 4 days, changing water once.
Using 2 cups of water for each cup of peel, slowly bring to boil and simmer gently until quite soft, stirring from time to time.
Strain the juice though double thick muslin without stirring or squeezing. This will cause the jelly to become cloudy. A good idea is to hang the cloth some distance above the bowl and leave to gently drip through. Be patient and give it time.
Measure the juice and and add 1 cup of sugar to each cup of juice.*
Stir well and bring to the boil along with 1 tablespoon lemon juice for each 2 cups of juice.
Boil rapidly in a large, open saucepan without stirring.
When it seems to start thickening, test by cooling the jelly in a stirring spoon and then allow to drop from the spoon. If the jelly falls in drops it is not ready. Once it flakes (or sheets) when being dropped, you are there. (You can also test by dropping a spoonful in a very cold (from fridge or freeaer) saucer. Allow to cool slightly and note whether it has firmed up by touching lightly. The temperature reached will be about 220 degrees.
Fill sterilized jars en seal with paraffin wax or (as I do) greaseproof paper rounds dipped in brandy.
*If you want to be sure that the jelly will be perfect, especially in large quantities, you can do the following pectin test before straining the juice through the muslim. Pour 1 tablespoon of the juice in a small glass containing a small amount of grain (ethyl) alcohol Carefully pour the kliguid into a small plate and note the firmness of the lump that has formed.
One distinct lump shows high pectin and you wil need 1 c sugar for 1 c juice.
If two or three smaller lumps are formed, you wil need three-quarter c sugar for 1 c juice.
If many small lumps form, you will have to use store-bought pectin. I have never found this necessary and prefer making jellies w/out the help of commercial pectin.
This soounds complicated, but once you get going, you'll be on a roll. Hope you succeed and enjoy it.
From sunny South Africa