• Rinse the blueberries thoroughly under cold water and remove any stems or leaves. Place the berries into a heavy-bottomed pot and lightly smash using the back of a wooden spoon or a potato masher. You want them to release some juice but still have some chunks for texture.
• Stir in the freshly squeezed lemon juice and the package of powdered pectin.
• Place the pot over medium-high heat and bring the mixture to a boil, stirring constantly to prevent burning. Once it starts boiling, continue to stir for about 1 minute to ensure the pectin is well distributed.
• Gradually stir in the granulated sugar. Continue stirring until the sugar is completely dissolved. Increase the heat to high and bring the mixture back to a rolling boil that cannot be stirred down. This is important for the jam to set properly.
• Let the mixture boil for 3 minutes, stirring constantly. You want the jam to reach a temperature of 220 degrees Fahrenheit. Using a candy thermometer can help you monitor the temperature accurately.

Prepare the Jars

• While the jam is cooking, sterilize your jars and lids. You can do this by boiling them in water for at least 10 minutes or running them through the dishwasher on a hot cycle. Once sterilized, carefully remove the jars and lids and place them on a clean towel to dry.

Process the Jam

• Carefully ladle the hot jam into the sterilized jars, leaving about 1/4 inch of space at the top. Wipe the rims of the jars with a clean, damp cloth to ensure a good seal. Place the lids on the jars and screw on the bands until they are fingertip tight. Process the Jars:
• Place the filled jars into a boiling water bath, ensuring they are fully submerged. Process the jars in the boiling water for 10 minutes to seal them properly. Adjust the processing time if you are at a higher altitude (check a reliable canning guide for specific times). Cool and Store:
• Carefully remove the jars from the water bath and place them on a towel to cool. Do not disturb them for 12-24 hours.
• Once cooled, check the seals by pressing down on the center of each lid. If it doesn't pop back, the jar is sealed. Store the sealed jars in a cool, dark place. Refrigerate any jars that did not seal properly and use them first.