4 1/2 c. mashed blueberries (1 1/2 qts. whole berries)
7 c. sugar
1 bottle liquid pectin
1 tbsp. lemon juice/vinegar
Dab of butter

Mix berries and sugar thoroughly. Add lemon juice or vinegar and butter. Bring to a boil on high heat and boil 1 minute while constantly stirring. Remove from heat. Add pectin. Stir briefly and skim off foam. Pour quickly into hot, sterilized jars. Seal with lids and simmer in boiling water bath about 10 minutes.