NOTE: While you are making the jelly, you will need to have at least 2 pots going at the same time (perhaps 3 if you are using smaller canning jars and can’t fit them nicely into one pot). Once the jelly comes together it will be hectic so you need to have everything set up in advance.
Prep:- Put all the jars into the pot(s) and cover with water- Have a space beside the stove open for the canning to happen (on a cooling rack or other heat safe surface)- Make sure you have tongs or jar lifters to safely pull the jars out of the water- Make sure your have the canning lids prepped and ready as well as a clean cloth to wipe the rims of the jars after filling- Measure out the sugar into a bowl and set aside- Pour the juice into a pot- If desired, you can place a plate in the fridge to cool so that you can test the thickness later) Turn on the elements under all the pots (the water will come to a boil in good time when you start it at the same time as the jelly, assuming you start with room temperature to warm water)
Add the pectin, attempting to minimize clumps (I started with a whisk while adding the pectin then switched to my usual wooden spoon once it was in)
Add a knob of butter
Bring the juice + pectin to a boil. Stir frequently to ensure it heats and thickens evenly.
Add the sugar, stirring while adding to avoid or break up clumps.
Bring the jelly back to a boil.
In the meantime, whenever the water comes to a rolling boil for the jars, turn it down to a simmer.
You can confirm that it is thick enough by dripping a little bit of the jelly onto the cold plate from the fridge. It should start to thicken fairly rapidly as it cools.