Heat a saucepan with 200 ml/ 6.8 floz lemon juice, zest of 1 lemon, 100 ml/3.4 floz water, and 225 grams/7.94 oz sugar. Bring to a boil over medium-low heat and stir until the sugar has dissolved.
Strain the syrup through a fine sieve to remove the zest. Pour into sterilized syrup bottles or an ice cube tray.
To make lemonade, pour a splash of syrup into a glass and dilute to taste with (sparkling) water, ice cubes, and optional fresh mint.
How to store
Freeze the syrup in an ice cube tray or store it in a sealed bottle in the refrigerator for up to one month. Drink the prepared lemonade right away or store it for up to two days in the fridge (stir before serving).