Place 2 saucers or small plates in the freezer, ready to check for the setting point of your marmalade.
Thoroughly wash the lemons. Remove each end of the lemons and cut the lemons into quarters lengthways. Holding two of the quarters together, slice as thinly as possible and remove any seeds.
Place the lemon slices in a non-reactive bowl. See Note 3. Add 6 cups of water, cover the bowl and leave the lemons to stand overnight.
The following day, place the lemons and water into a large, non-reactive saucepan. – See Note 4.
Over medium-high heat, bring the fruit and water to the boil. Boil for approximately 15 minutes or until the lemon peel is tender, stirring occasionally with a long-handled wooden spoon. – See Note 5. The time may vary slightly depending on the variety of lemon and the thickness of the slices.
Add the sugar and stir well to dissolve it. After dissolving the sugar, return the fruit to the boil, stir occasionally and skim to remove any foam. Continue to stir until the marmalade reaches setting point, about 20 minutes. – See Note 6Remove from the heat to conduct the wrinkle test. If not set, continue to boil for another 1 minute and then test again. To test for setting point, I use the “wrinkle” test. Take one of your saucers from the freezer and pour a small amount of marmalade onto it. Let it cool for a minute then push against the marmalade with the tip of your finger. If the surface wrinkles it means setting point has been reached. Alternatively, if you are not confident checking this way or are not experienced at making marmalade, you can use the fail-safe method of using a jam/candy thermometer which you clip to the side of your saucepan. When attaching your thermometer, make sure that the base is not touching the bottom of the saucepan. Your marmalade has reached setting point when the temperature reaches 104.5 degree C or 220 degrees F. It will still be liquid at this point, and will set as it cools.
Take the mixture off the heat and let the marmalade stand for about 10 minutes. This will help evenly distribute the fruit throughout the jars.
Remove your jars from the oven and carefully ladle the marmalade into the heated, sterilised jars. You need to be very careful. Splashing yourself with hot marmalade will result in a very serious burn. I suggest you have clothing with long sleeves and ensure that you do not have children nearby. Put lids on jars immediately, and seal well - being careful to use a cloth or oven gloves to handle the jars/lids.