1 Prepare four to six lemons (you can add more lemons if you like acid).
2 Rub the lemon skin with salt, soak it in salt water (about half an hour), and remove the seeds from the soaked lemon slices.
3 Put the aged lemon with rock sugar into a saucepan and add water to boil (about 10 hours). There is no saucepan, so you can put the aged rock sugar lemon in the casserole. Sit in a big iron pot and boil it with water. (It will be a little sticky when the color turns dark red, and it will be more sticky after cooling.