Remove the flesh and the rind leaving just the white part of the watermelon.

Cut it into small pieces and place it in a pot with 2 cups water over strong heat until you see that the pieces have become somewhat translucent.

Blend the pieces in a food processor.

Place them back in the pot once more over medium heat with the sugar, the lemon, the cloves and the vanilla.

Stir and let it cook until the jam sets.