Place blueberries into a large pot or salad spinner.

Fill a colander with water and rinse the blueberries thoroughly until the water runs clean.

Repeat the same with the blackberries.

Place half of the berries into a pot and add about ¼ cup of sugar.

Use a potato masher to mash the berries with the sugar.

Repeat with the remaining berries.

Cover the pot and let it sit for a minimum 4 hours to allow the sugar to draw out the juices from the berries.

After the resting period, there should be plenty of berry juices in the pot. Bring the berries and their juices to a boil over medium heat, stirring often to dissolve the sugar.

Once boiling, lower the heat to medium-low and cook the berries for 15 minutes.

Turn off the heat and use a fine mesh strainer or jelly bag to strain the berry juices into a separate pot.

Discard the berry pulp or use it to make a summer drink by mixing it with hot water.

Mix ¼ cup of sugar with the pectin and set aside. This will help the jelly set.

Add the remaining sugar to the strained berry syrup and bring it to a boil. Don’t worry about the foam forming on the surface of the cooking jelly, it will subside.

Once boiling, reduce the heat to medium and add the sugar-pectin mixture

Mix well to ensure the sugar and pectin are fully incorporated.

Cook for an additional 15 minutes. Perform a chilled plate test to check the jelly consistency. Cook for 5-10 minutes more if you prefer a thicker jelly.

Pour the hot blackberry blueberry jelly into clean, sterilized canning jars.

Process the jars using your preferred canning method.