Step 1: Prepare the Blackberries

1. Rinse the blackberries under cold water and remove any stems or leaves.
2. Place the blackberries in a large pot and crush them with a potato masher or fork to release their juices.

Step 2: Cook the Blackberries

1. Add the water to the pot with the crushed blackberries.
2. Bring the mixture to a boil over medium-high heat, stirring occasionally.
3. Reduce the heat and let it simmer for 10-15 minutes, or until the blackberries are soft and the mixture is juicy.

Step 3: Strain the Mixture

1. Place a fine-mesh strainer or cheesecloth over a large bowl.
2. Pour the cooked blackberry mixture into the strainer, pressing gently with a spoon to extract as much juice as possible. Discard the seeds and pulp.

Step 4: Prepare the Jelly Base

1. Measure out 3 1/2 cups of blackberry juice and pour it into a clean, large pot.
2. Stir in the lemon juice and powdered pectin until fully dissolved.

Step 5: Boil the Mixture

1. Bring the blackberry juice mixture to a rolling boil over high heat, stirring constantly.
2. Add the sugar all at once, stirring until it dissolves completely.
3. Return the mixture to a rolling boil and let it boil for exactly 1 minute, stirring continuously.

Step 6: Test for Doneness

1. To check if the jelly is ready, perform a spoon test: Dip a cold spoon into the mixture and let it cool slightly. If the jelly coats the spoon and forms a gel-like consistency, it’s done.

Step 7: Jar the Jelly

1. Remove the pot from the heat and skim off any foam from the surface.
2. Carefully ladle the hot jelly into sterilized jars, leaving 1/4 inch of headspace at the top.
3. Wipe the rims of the jars with a clean, damp cloth to remove any spills.
4. Seal the jars with sterilized lids and rings.

Step 8: Process the Jars (Optional)

1. For long-term storage, process the jars in a boiling water bath for 10 minutes.
2. Remove the jars and let them cool completely on a towel. Check the seals by pressing the center of the lids—if they don’t pop, the jars are properly sealed.