1. Rinse the mosphila thoroughly, drain them and place them in a large saucepan. Add the water and bring to the boil. Reduce the heat, cover the saucepan and simmer for approximately 1½–2 hours, or until the mosphila are very soft.
2. Allow the liquid to cool completely. Ideally, leave it to rest for 8–12 hours. Gently press the fruit to release its pectin and strain the liquid. For a clearer result, line the strainer with cheesecloth or muslin. Press the mosphila to extract their juice.
3. Measure the juice and pour it into a large, deep saucepan. Place over the heat and bring to the boil. Add the sugar, using a ratio of 1 cup of sugar for every 1 cup of mosphilo juice.
4. Stir until the sugar dissolves and add the rose geranium leaves. Boil over high heat for approximately 35–40 minutes. Add the lemon juice and continue boiling for another 5–10 minutes.
5. Occasionally skim off any foam that forms on the surface using a slotted spoon. When the jam begins to set, carefully remove the rose geranium leaves.

How to check if the jam is ready

1. Using a thermometer: The temperature should reach 115°C. At this stage, add the lemon juice and boil for another 3–4 minutes.
2. Using a wooden spoon: Scoop up a little of the liquid and pour it back into the saucepan from above. It should no longer be runny; it should be well set and fall in thick drops. As my grandmother used to say, “it should fall knot by knot.”
3. Using a chilled saucer: Place a saucer in the freezer until it is very cold. Spoon a little jam onto it and leave it to cool for a few seconds. Run the back of a spoon through the middle. If the two sides do not run back together, the jam is ready.
4. Pour the jam into sterilised jars, allow it to cool and seal the jars tightly.
5. To sterilise the jars, wash them in the dishwasher or rinse them thoroughly and place them upside down on the oven rack. Heat the oven to 100°C and leave the jars inside for 20 minutes.