To begin, combine the pomegranate juice and lemon juice in a large, non-reactive pot.
Slowly whisk in the pectin.
Add in the butter.
Heat the mixture to a boil, stirring continually. Boil for 1 minute.
Add the sugar, and bring the mixture back up to a rapid boil. Boil for 1 minute.
Remove it from the heat and remove any foam that may be there. (The butter prevents most or all of it.) Immediately ladle the jelly into hot half-pint canning jars, leaving 1/4 inch of headspace.
With the rims of the jars with a damp cloth that has been dipped in white vinegar.
Place a lid and ring on the jar and place the jar in the hot water bath or steam canner. Do this with all of the jars.
Process the jars for 10 minutes. (See the note about adjusting time for elevation in the article above. Processing times for canning recipes are always give for under 1000 ft elevation. You must make adjustments if you live at a higher environment.)
After the jars have processed, turn off the heat, remove the lid of the canner and let the jars rest for 5 minutes.
Transfer the jars to a line surface in a draft-free location and let them sit for 12-24 hours.
Remove the rings, test the seals and label the jars. Store them away in the pantry.