Place the blackcurrants and jostaberries in a large pot or salad spinner. Fill it with water and let the berries soak for 5 minutes to loosen any debris and leaves. Rinse thoroughly until the water runs clear.

Because we only need juice for this preserve, there’s no need to remove the stems and blossom ends from either the blackcurrants or jostaberries.

Place the blackcurrants and jostaberries into a suitably sized pot and add roughly one-third of the sugar required for this recipe.

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

Cover the pot and let it sit for at least 8 hours or overnight. This allows the sugar to draw out the juices from the berries, which is essential for making the jelly.

After the resting period, you should see 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.

Don’t worry about skimming the foam at this step.

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

Turn off the heat and use a fine mesh strainer to strain the blackcurrant and jostaberry juices into a separate pot. We will use these juices to make the jelly. You can discard the berry pulp or use it to make a crusty pie.

First, mix the remaining sugar and pectin together and set aside.

Pour the strained blackcurrant and jostaberry juices back into the pot and bring it to a boil.

Once boiling, reduce the heat to the lowest setting and let the liquid simmer for 10 more minutes.

As the liquid simmers, remove any impurities that form on the surface.

Add the sugar and pectin mixture to the simmering blackcurrant jostaberry liquid. Stir vigorously to ensure the sugar and pectin are well incorporated into the mixture.

Cook for an additional 15 minutes. If desired, perform a chilled plate test to check the jelly's consistency. Cook for 5-10 minutes more if you prefer a denser jelly.

Pour the hot jelly into clean, sterilized canning jars. Process using your preferred canning method.