Scrub lemons and zest four of them. Bring a saucepan of water to the boil, add lemons and leave for 1 minute. Lemons are often quite hard and unyielding - this softens them so they give more juice when squeezed.

Remove lemons and reserve lemon-infused water. Juice lemons. Put sugar, lemon zest and 500 millilitres lemon-infused water into a saucepan. Heat gently to dissolve sugar, then bring to the boil.

Add 500 millilitres lemon juice and bring just to boiling point. Remove from heat and strain through a sieve into a jug.

Pour immediately into hot, sterilised bottles and seal immediately with sterilised screw caps, corks or swing-top lids.

Leave to cool, then store cordial in a cool, dry place or in the fridge for up to 4 months. For longer storage - up to a year - sterilise the bottles in a water bath*. To serve the cordial, mix 1 part syrup to 4 parts water.

Note Another way to increase the yield of juice from citrus fruits is to roll the fruit back and forth over a work surface, pressing down firmly with the palm of your hand, for 2-3 minutes.

* To sterilise jars and bottles, put them through a short dishwasher cycle, then use immediately while still warm. To sterilise in a water bath, put the glassware in a pot and fill with water, bring to a simmer and simmer for 5 minutes. Remove while warm, drain water and keep in a clean place until needed.