Place the sugar, juniper berries and bitter lemon in a pan, bring up to a simmer and simmer gently for five minutes then remove from the heat and leave to cool. Stir in the lemon juice and gin and refrigerate until cold.

Gently whisk the egg white in a large jug until just frothy then pass the lemon mixture through a sieve into the jug and whisk to combine. Churn in an ice cream maker according to the manufacturers instructions; it will not freeze as firmly as usual due to the gin but should reach at least a thick slushy texture.

Transfer to a freezer-proof container and freeze overnight, it will remain a soft-serve consistency but will become firmer (unless you don't have a very powerful freezer in which case you may need to use less gin).