1. Use a sharp knife to remove ends from the limes and lemons. Slice the limes very thinly. Remove the rind from the lemon and cut away the pith. Finely slice the lemon rind, ensuring you retain all the juice. Roughly chop the lemon pulp. Combine rind, pulp and juices in a large heatproof bowl. (Citrus fruit should weigh about 450g).
2. Pour boiling water over fruit. Allow to stand overnight.
3. Place a saucer in the freezer. Pour soaked fruit into a large wide based saucepan. Bring to the boil, reduce heat and simmer for about 30 minutes.
4. Add jam setting sugar, stirring over a medium heat for 1 minute or until sugar dissolves. Bring to the boil and boil for 3 - 4 minutes (removing any scum or foam with a metal spoon).
5. You can start testing at 3 minutes. Setting time will vary depending on saucepan size and heat of hot plate.
6. Test a small amount of marmalade on a cold saucer at 3 minutes (the surface should wrinkle when a spoon is pushed through it).
7. Ladle hot marmalade into sterilised jars and screw on lid to seal. Turn upside down for 5 minutes to draw a vacuum. Turn upright and set aside until cooled. Label, date and store in a cool, dark place. Refrigerate after opening.
Makes 2 x 200ml jars.