How to Make It
Sort and rinse blackberries. Pulse blackberries in a blender or food processor until finely chopped. Press through a fine wire-mesh strainer or cheesecloth to remove seeds. Cook blackberries and sugar in a heavy medium saucepan over medium-high heat, stirring constantly, until sugar dissolves. Stir in pectin, and return to a boil; boil, stirring constantly, 5 minutes or until mixture thickens. Remove from heat, and skim off foam with a metal spoon.
Quickly pour hot jelly into hot, sterilized jars, filling to 1/4 inch from top; wipe jar rims. Cover at once with metal lids, and screw on bands. Process in boiling-water bath 5 minutes.