Prepare the Fruit: Wash the blackberries thoroughly and mash them using a potato masher or fork until you reach a chunky consistency.
Cook the Jam: Combine the mashed blackberries, sugar, and water in a large pot. Stir well and bring the mixture to a boil over medium-high heat. Stir occasionally to prevent burning.
Add Pectin: Once the mixture is boiling, add the fruit pectin and lemon juice. Stir until the pectin dissolves, and let the mixture simmer for 10-15 minutes, allowing it to thicken.
Test the Consistency: Drop a small spoonful of jam on a cold plate and let it sit for a few seconds. If it wrinkles and holds its shape, it’s ready. If not, continue cooking for a few more minutes.
Jar the Jam: Once the jam reaches the desired consistency, pour it into sterilized jars, leaving about ¼ inch at the top. Seal with lids and allow the jars to cool completely.