Gather supplies, wash jars, and simmer lids.

Add juice and pectin in a large pot. Heat on High. Stir until pectin is dissolved. Add butter if desired. Bring to a rolling boil.

Stir in full measure of sugar all at once.

Return to a full roiling boil that can't be stirred down and cook for 2 minutes while stirring constantly.

Ladle into clean glass jars. I like to use pints for my family, because we go through it fast, and pretty half pints for gifts.

Wipe rims. Place lids (that have been simmered) on jars and screw bands over the top, finger tip tight.

Process for 5 minutes, adjusting time to your altitude. Remove jars and cool completely, then let stand for 24 hours.

Keeps about a year, if it doesn't get devoured by then.