Begin by making the sugar syrup by adding 200g of caster sugar and 250ml of water in a pan. Dissolve the sugar in the water and then allow to cool. Any remaining sugar syrup can be kept in the fridge for a later date.
Fill a jug with ice and add the lemon juice and sugar syrup. Mix well, then add the lemon slices and top up with sparkling water. Garnish with fresh mint to serve, if you like.
To give this cocktail a grown-up kick, add 50ml (2fl oz) of gin or vodka. Rum or tequila will also work well.
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