Measure exactly 3-3/4 cups juice into 6- or 8-qt. saucepan.
Stir pectin and butter into juice in pan. Bring mixture to full rolling boil (boil that doesn’t stop bubbling when stirred) on high heat, stirring constantly. Stir in sugar. Return to full rolling boil and boil 1 min., stirring constantly. Remove from heat.
Skim off any foam. (If you will let the jelly sit for a couple of minutes, it is easier to remove the foam). I carefully run my spoon over the top of the jelly and try to push it into a small area (see above photo) which makes it easy to remove.
Ladle immediately into prepared jars, filling to within 1/4 inch of tops. Wipe jar rims and threads. Cover with two-piece lids.
Process 10 min.