1 package powdered pectin (1.75 oz) (I use Sure Jell)
Prepare ground cherry juice by husking and washing ground cherries, then running them through a food processor.
Cook ground cherries gently for at least 15 minutes, until very soft. Drain through jelly bag for several hours or overnight. Avoid squeezing bag to keep juice clear.
Grate one tablespoon of zest from 1-2 lemon(s). Juice the lemon(s) to obtain ½ cup juice (you either need a large lemon or lemons or can substitute a little bottled juice to make up the difference).
Sterilize seven 8-ounce jars, keep hot. Prep rings and lids. Fill water bath canner and bring to boil.
Measure sugar and set aside. Combine juices and zest, stir in pectin and butter. Bring to full rolling boil over high heat, stirring constantly. Immediately add all of the sugar. Bring back to full rolling boil and boil 3 minutes, stirring constantly.
Ladle jam into sterilized jars leaving 1/4″ headspace. Wipe rims clean and screw on the lids. Process for 10 minutes in water bath canner (add 1 minute for every 1,000 feet above sea level). Makes around 7 half pint jars.