Wash (11-12) jars and screw bands in hot soapy water; rinse with warm water, or in the dishwasher. Pour boiling water over flat lids in saucepan off the heat. Let stand in hot water until ready to use.

Crush blackberries thoroughly, one layer at a time.

STIR pectin into fruit mixture in saucepan. Add butter to reduce foaming, if desired. Bring mixture to full rolling boil (a boil that doesn’t stop bubbling when stirred) on high heat, stirring constantly. Stir in sugar.

Return to full rolling boil and boil exactly 1 minute, stirring constantly. Remove from heat. Skim off any foam with metal spoon.

LADLE immediately into prepared jars, filling to within 1/8 inch of tops. Wipe jar rims and threads.

Cover with 2-piece lids making sure your lids are dry. Screw bands tightly. Place jars on a cool dry surface.

After jars cool, check seals by pressing middle of lid with finger. (If lid springs back, lid is not sealed and refrigeration is necessary.)

You will hear the tops popping when they start to cool. This means they are sealing.