Step #1 Slice the lemons, including the rind, thin, seeds & all, & place into a saucepan.
Step #2 Core the apples, but do not peel, & chop coarsely.
Step #3 Add the apples to the pan & pour in enough water to just cover the fruit.
Step #4 Cook over moderate heat, until the fruit becomes mushy.
Step #5 Pour the mixture into a jelly bag or a colander lined with several thicknesses of damp cheesecloth & let drip into a bowl for about an hr.
Step #6 Using a spoon, force as much liquid through the cheesecloth as possible.
Step #7 Measure the juice; you should have about 4 c.
Step #8 For each c of juice, add 3/4 c of sugar.
Step #9 Return to the pan & boil for another 15 mins or so, until the mixture reaches the jelly stage, about 220- to 225-degrees F on a candy thermometer.
Step #10 To be absolutely certain, place a tbsp of the hot mixture into a saucer & set it in the freezer for a few mins.
Step #11 If it jells, the mixture is ready.
Step #12 Pour the jelly into HOT, sterilized jars & seal.
Step #13 Process in boiling water bath for 10 mins.
Step #14 Or it may be store this in a covered container in the refrigerator for several months.