- In a saucepan, cover the lemons with cold water. Bring to a boil, then simmer for 30 minutes or until the lemons are tender, stirring several times during cooking. Drain and rinse under cold running water. Let cool for a few minutes.
- On a work surface, cut the lemons in half. Remove and discard the seeds, then finely chop the lemon peel and flesh. Return to the saucepan. Add the sugar and water.
- Cook over medium heat until a candy thermometer reads 223°F (106°C), about 20 minutes. Transfer to airtight containers or jars.
- To sterilize the jars filled with marmalade, completely cover with water and boil for 10 minutes. Sterilized jars will keep for 1 year at room temperature, unsterilized for 1 month in the refrigerator.