If you plan to can your jelly, prepare a water bath canner by completely covering eight 4-ounce mason jars with water, then boiling them for 10 minutes. Keep the jars in the hot water until needed. The lids can be added a few minutes before you need them.
Prepare Jelly
Wash saskatoons and remove any stems as well as dried or underripe berries. Add to a six-quart Dutch oven and cover with 4 cups of water. Bring to a boil, then simmer, uncovered, for 20 minutes. Smash the fruit with a masher to release the berry juice.
Strain the berry juice through a fine sieve lined with a few layers of cheesecloth, or use a jelly bag. You should have approximately 3 cups of juice. If not, add enough cherry or cranberry juice to equal 3 cups total.
Clean Dutch oven and return to the stove. Pour strained juice back into it. Turn heat up to medium, then whisk in RealFruit Classic Pectin until dissolved. Bring to a hard boil for one full minute. Skim foam from surface. I like to use a skimmer to do this.
Add lemon juice and sugar, then whisk over medium heat to dissolve. Return mixture to a full rolling boil for two minutes. Turn off stove, then ladle jelly into sterilized jars, leaving ¼-½" headspace. Wipe rims with a clean damp cloth or paper towel and hand-tighten collars.
Canning Instructions
Add jars to a hot water canner and make sure the water level is at least a few inches above the jars. Process the filled jars in boiling water based on the processing time by elevation chart in this post.
Notes
Jelly needs to fully cool to set and may take up to 24 hours. Don't move the jars until the jelly has set.
It is generally recommended to let the berry juice drip into the bowl, undisturbed. Squeezing the berries may cause the jelly to be cloudy. I squeeze the fruit to extract as much fruit as possible, and no one has complained yet!
Store unsealed jars in the fridge for up to a few months or until consumed.
Sealed and processed serviceberry jelly can be stored in the pantry for up to a year.