Put all the ingredients except the starch and the water in a saucepan and let everything boil. Mix the starch with the water and pour it into the simmering mass. Mix everything well and wait until the starch thickens. It`s best to try a little with the amount of sugar and starch, depending on how sweet or firm you like it. Put the lemon curd in a screw-top jar while it is still hot, put the lid on it and put it in the fridge. The whole thing should last a few weeks there.