If canning, prepare canning equipment.
Measure sugar in a large bowl and set aside. (It’s super important, when working with powdered pectin, to add the sugar all at once; otherwise, the jam may not set properly.)
Combine maypop juice and lemon juice in a large stainless steel saucepan, and whisk in the pectin until it is fully dissolved. Bring the mixture to a full rolling boil, stirring frequently to prevent burning.
Add the sugar to the boiling mixture all at once, stirring constantly to combine, and return to a full rolling boil that doesn’t go down when you stir. Allow the mixture to boil for 1 full minute, stirring constantly.
If canning, follow hot-water bath canning procedures, leaving ¼ inch headspace between the jam and the lid. Process jars in a hot-water bath for 10 minutes. Wait 5 minutes, then remove the jars from the canner, and allow to rest, upright and undisturbed, for 24 hours before testing the seals.
