Be sure the see the first post (How to find and gather) and the second post (how to prepare the fruit and juice).
If you have not made jelly before, please do the safe thing and read up on specific canning methods, with up-to-date instructions before making this. The National Center for Home Food Preservation (linked from my sidebar) is a good place to go to start learning. If you have a dear one who knows how to can, call them and enlist their advice. Call your mom anyway, just for general principles.
Jelly is one of the easiest and safest home-canned foods you can make. I follow the instructions that come in the package of Sure-Jell, which is the brand of powdered pectin I usually use. For this batch I used Can-Jel, which is Kroger's brand, and it came out just fine. "Pectin" is a naturally occuring substance that causes fruit juice to gel when it is cooked with sugar. Apples, especially the peelings, have a great lot of it.
I always add extra pectin to my jellies and jams. I don't use liquid pectin, only the powdered type. However, my recipes all call for powdered pectin - be sure to use the type that your recipe calls for. It does make a difference!
Gather your jars, wash them and sterilize them with boiling water: either put the jars (jars only NOT the lids) in a pot of boiling water for 10 minutes (use canning tongs to remove them), or run them through your dishwasher's "sterilize" cycle. I always sterilize one extra jar just in case I need it.
Set them on an old towel in a handy location so that you will be able to easily ladle the hot liquid jelly into them when the time comes. Right next to the stove works best for me, and is safest. You do not want to be carrying a pot full or even a jar-full of boiling liquid jelly. The towel under the jars is to catch spills.
The Prickly Pear Jelly recipe I use is very similar to recipes for elderberry jelly. It makes about 11 half-pints. Since this recipe calls for 2 boxes of pectin, you could half it but do not double it.
If you need more, make 2 batches. Use only sugar for this recipe - do not reduce the amount of sugar and do not use sugar substitutes.
Only make jelly when you can give it your full attention from start to finish. It won't take long for the actual cooking and putting up but you cannot leave it once you start. So get everything else done in advance, but make sure you have an hour of uninterrupted time and turn the phone off before you turn the stove on.
You will need:
6 cups of prepared Prickly Pear Juice
1/4 cup lemon juice (either fresh or bottled)
9 cups of sugar
2 boxes of powdered pectin
1/2 tsp of butter or margarine (to reduce foaming)
Put your jar lids (the seal part) into a sauce pan of water and heat to boiling. Turn the fire down and keep warm.
Measure the sugar into a large bowl and set aside.
Measure 6 cups of prepared juice into a large spaghetti pot and add 1/4 cup lemon juice. Add both packages of pectin and whisk or stir well. Add 1/2 tsp butter - this will help keep the foam down once the jelly starts boiling hard.
Cook on high heat, stirring constantly, until it comes to a full rolling boil that cannot be stirred down.
While stirring, pour all of the sugar in all at once, and keep stirring over high heat until it comes back to a full rolling boil.
Don't take your eyes off it at this point.
Once it is at a full rolling boil, boil it hard for one full minute - this is important, use your timer if you can.
Turn the stove off and remove from hear and keep stirring until the boil dies down. If there is foam on the top, use a metal spoon to skim it off and discard it (I put it into a bowl and use it as my first taste after all the jars are sealed, but you shouldn't have much foam if you put the butter in).
Ladle the jelly into jars to within 1/8" from the top. When they are all filled, wipe off the rims with a wet cloth.
One at a time, get the lids out of the hot water with tongs and put lid and ring onto the jar. Tighten as tight as you can and set back down on a level surface away from drafts.
Repeat with all the jars, setting them close together so they will cool slowly. In about half an hour to an hour you should start hearing the sweet sound of lids popping as they seal.
Don't disturb them til the next day, then you can set them into a sink of clean water and finish getting the jelly off the outside, dry off and label. If they have sealed, they will keep for years.
If the seal didn't tighten they will still keep a long time, but you could either refrigerate those or process them in a boiling water bath if you want (per the recommendations of the NCHFP). Until recently -- oh sometime last week I'm sure -- we sealed jelly with paraffin wax and kept it until we used it up!