Rinse blackberries with cold water. Place them in pot. Cover them with sugar. Bring to a simmer and cook for about 20 minutes. Turn off and set aside, let it cool down
Repeat the process of cooking for about 5-7 more time, or until you reach the desired thickness. As it simmer, stir the jam occasionally to prevent burning. Repeat util you reach desired constancy. Keep in mind, jam does thicken as it cools down.
CANNING blackberry JAM
Sterilize your jars to prepare them for canning. Preheat oven to 215°F. Wash the jars and lids with soap and water. Place jars directly on the oven rack. Allow them to bake for 20 minutes, or until they are completely dry and free of water droplets.
Once you bring your jam to its last boil, add piping hot jam directly into the hot, sterilized jars. Cover each jar with a lid. Turn the jars upside down and let them sit at room temperature for an hour. Store jars in a cool place.