7 (about 1.3 kg) Granny Smith apples, peeled, cored and sliced2lemons, juice only, seeds reserved450 gmcaster sugar 2 tbsprosemary leaves
Combine apples, lemon juice and seeds in a large saucepan. Cover with 1 litre water, bring to boil over medium heat, then reduce heat to low and simmer for 1 hour.
Transfer mixture to a muslin-lined fine sieve and strain into a bowl, discarding pulp. This should yield about 2 cups of liquid.
Combine liquid and sugar in a large saucepan and bring to the boil, stirring to dissolve sugar and cook for 15-20 minutes. Test whether jelly is set. If not, return to heat and test after 5 minutes. Remove from heat, stand for 10 minutes, then skim scum from surface. Add rosemary and ladle into clean, dry jars. Seal lids, invert jars for 2 minutes, then turn upright and cool completely. Store in the refrigerator for up to 3 weeks.