Cut the de-seeded water melon into small pieces and add to the pot in which you are going to make the jam. Add the powdered sugar and mix well. Let it sit for half an hour. The amount of sugar will vary according to the sweetness of the watermelon and personal preference. After the watermelon and sugar have sat for half an hour, put it on the stove and allow to cook. Constant stirring is needed to avoid the mixture sticking to the bottom of the pot. I prefer chunks of fruit in my jam, but if you don’t, now is the time to get your masher out and mash the chunks
Alternately, you can purée the fruits before starting itself and avoid the half hour of soaking at the start. After about ten minutes of cooking, add the lemon juice and chia seeds (optional). Continue stirring till the jam reaches the required consistency. Please remember that it will thicken after cooling so take it off the stove when it still has some syrup in it. Add the vanilla extract (optional) and mix well, allow to cool and store in the fridge. It is recommended that you store the jam in the fridge, but I have left mine outside for a month and it was fine. Enjoy. Makes a 200 gm jar of jam.