Place the zest or peel of the lemons into a sterile glass jar, pour in the alcohol and cover with baking parchment. Let sit for 36 hours at room temperature.
After 36 hours combine water and sugar in a saucepan and boil until thickened into a syrup. Let the syrup cool and add to the bottle with the alcohol and lemon zest. Serve chilled.
It may be preferable to use organic lemons. Try not to get any of the white pith in your limoncello as this can result in bitterness.
Traditionally limoncello is made with 190-proof grain alcohol. As this can be hard to find in the UK, in a pinch you can try substituting a high proof vodka instead, although keep in mind that this will taste different to an authentic limoncello. Look for high-proof alcohol at some off-licences or speciality shops carrying Polish goods.