Combine ingredients: In a large saucepan, combine the blackberries, sugar, lemon juice, and pectin.

Bring to a boil: Bring the mixture to a boil over high heat, stirring constantly.

Simmer: Reduce heat to low and simmer for 10-15 minutes, or until the jam thickens.

Test for set: To test if the jam is set, drop a small amount onto a chilled plate. If it doesn't spread, it's ready.

Can the jam: If you want to can the jam, sterilize your jars and lids. Ladle the hot jam into the jars, leaving about 1/4 inch of headspace. Wipe the rims of the jars and seal them with the sterilized lids.

Water-bath canning: Place the filled jars in a large pot and add enough hot water to cover them by 1 inch. Bring the water to a boil, then reduce heat to a simmer. Simmer for 20 minutes for half-pint jars or 30 minutes for pint jars.

Remove and cool: Remove the jars from the water bath and let them cool completely before storing.