I have made an identical recipe twice in the last three weeks! This jelly is absolutely brilliant - in my opinion no other jam/jelly can get close to it for sheer flavour and colour. Quinces in Qld cost $2.50 EACH! so JustJan is a very lucky lady.
It is very easy to make but a word of warning. If you are a devotee of using a sugar thermometer as I am be very careful because there is every chance that the jelly will have got to its set point before the standard 105-106C.
Take it off the heat as soon as it gets close and do not leave it sitting about in the hot saucepan or on the hot hob either or else you may well have a fruit cheese on your hands. If it has not jelled by next day bring it to the boil again and repeat the getting off the heat as soon as it has boiled. You will probably find that it sets perfectly. Repeat if you have to by giving it one quick boil at a time until you are happy.
This is the voice of hard experience from last year speaking. We still have not finished all the quince paste/fruit cheese I made last year without intending to - but that also is delicious with cheese and crackers. Goodluck, John