4 cups blackberries, packed
7 cups sugar
½ teaspoon butter
1 packet liquid fruit pectin
Combine the blackberries, sugar, and butter in a large pot (about 8 quarts). Crush the berries with a potato masher and bring to a full rolling boil that does not stop, even when stirred. Add the pectin and bring to a full rolling boil again and let boil for exactly 1 minute.
Ladle the hot berry mixture into sterilized jars* and cover with sterilized caps. If you are canning, place the jars in a large pot of boiling water. They should be covered by 1-2” of water. Reduce to a low boil and process for 10 minutes. Remove and place on a kitchen towel on the counter and let cool completely. If they are properly canned, you will hear the tops ‘pop’ in the next hour and when you press the lids in the center with your finger they will not bounce back.
If you are not canning, the jam will keep in the fridge for up to 2 months.
*To sterilize your jars, place them in a large pot of boiling water. Let them boil for 8-10 minutes. Carefully remove with canning tongs and place upside down on a clean wire rack over a kitchen towel. Place the tops in a small pot of boiling water and boil for 2 minutes. Turn off the heat and leave them in the hot water until ready to use.