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.