Cut the tomatoes into quarters and finely chop the chilli. Place both in a saucepan along with approx. 50 ml water. The water is just to keep the tomatoes from sticking to the pan. Bring the mixture to a boil and add the sugar. Boil until the liquid has reduced completely. Give it a whiz with a handheld blender before seasoning to taste with salt and lemon juice. Cool completely before serving. Store the jam in scalded jars and in the refrigerator to prolong the shelf life. If you make a large portion, rinse the jars with some sodium benzoate first. This improves their shelf life even more.