Wash the oranges and lemons thoroughly, then dry them in a clean tea towel. Pour 2 litres cold water into a large, wide pan or preserving pan.

Squeeze the oranges and lemons, adding the juice to the pan of water through a sieve, which will catch the pips - there are loads of pips in Seville oranges.

Using a metal spoon, scrape the pith and pips into the sieve holding the pips over the pan.

Tip all the pips and pith of the fruit from the sieve into the piece of muslin and tie securely. Put this into the pan.

Now comes the tedious bit, shredding the orange skins. I also pared the zest from the lemons and added those. Cut the orange rind halves into pieces and then slice with a sharp knife. If you like chunky marmalade you can keep the pieces quite thick but I like a thin shred so I cut them pretty finely.

As you slice, add the peel to the pan, and once you've done about half of the oranges you can put the pan on a medium heat to start the cooking process as it will take a while to come to the boil. When the liquid is boiling and all the peel is shredded, turn the heat down and simmer for two hours, uncovered, until the peel is translucent and the liquid has reduced by about half.

While the marmalade is simmering, sterilize your jars by washing in very hot water, or in a dish washer and placing in the oven with their lids. Put the oven on to 160°C/Gas 3, when it reaches that temperature turn the oven off but leave the jars inside.

Remove and discard the bag with the pips and pith, squeezing as much juice as possible back into the pan with the back of a wooden spoon.

Add all the sugar to the pan and stir over a low heat until it has dissolved. Increase the heat and boil rapidly until it reaches setting point. This usually takes about 15 minutes. Keep stirring to prevent anything sticking and burning at the bottom of the pan, be careful it's really hot and can bubble up and splash you if it goes for too long without being stirred.

Put two plates in the freezer. To test, remove the pan from the heat and spoon a little marmalade onto a chilled plate. Allow to cool for a few seconds, then push with a finger.

If the surface of the marmalade wrinkles it is ready. If not, boil for a further 5 minutes and test again. Turn off the heat and allow the marmalade to stand for 15 minutes.

Take the jars out of the oven and stand on a wooden board. Use a heatproof jug or a ladle to fill the jars with marmalade.

Wait until completely cool before putting the lids on, otherwise condensation will form inside and the marmalade won't keep. Store in a dark, cool place. Eat for breakfast on thickly buttered toast.