Prepare home canning jars and lids according to manufacturer’s instructions for sterilized jars. Keep jars hot until filled. Always use new lids.
Place berries, lemon juice, butter and pectin in a large pot. Bring mixture to full rolling boil, stirring constantly. Stir in sugar. Return to a full rolling boil and boil exactly 1 min., stirring constantly.
Remove from heat and skim off foam. Quickly ladle into the hot jars, leaving ¼-inch of head space at the top. Use a damp cloth to wipe any drips from the top and sides of the jars. Cover with hot lids and tighten rings firmly.
Set the hot jars on a rack in a canner or in a large pot of boiling water. The water needs to cover the jars by at least 1-2 inches. Boil the jars for 10 minutes.
Remove the jars from the boiling water and set on a towel or rack to cool overnight (but not more than 24 hours).
When cool, check the seals. The lids should be down in the center or stay down when pressed. Store in a cool, dark, dry place. Unsealed jars should be refrigerated and used within 3 weeks.