Greek-Style Lemon Sorbet

Finely grate the zest from 3 of the lemons directly into a medium saucepan — do this before juicing, as it is much easier to zest a whole lemon than a squeezed one. Add the caster sugar and water to the saucepan. Place over medium heat and stir until the sugar has completely dissolved. Bring to a gentle simmer and cook for 3 minutes until the syrup is clear and slightly thickened. Remove from the heat and leave to cool completely — a hot syrup added to the lemon juice will cook it and dull its fresh, bright flavour. While the syrup cools, juice all the lemons to get 200ml of fresh lemon juice. Strain the juice through a fine sieve to remove any pips and pulp — a clear juice produces a cleaner, more elegant sorbet. To prepare the lemon shells for serving: cut a thin slice from the base of 6 lemons so they sit flat without tipping, then cut off the top third of each lemon and scoop out the flesh and membrane with a small spoon, leaving a clean, intact shell. Place the shells in the freezer while you make the sorbet — they need to be frozen solid before the sorbet is spooned in.

Once the syrup is completely cool, combine it with the strained lemon juice in a large bowl or jug and stir well. Taste the mixture — it should be intensely lemony and quite sharp, noticeably more tart than you want the finished sorbet to taste, because freezing dulls sweetness and sharpness slightly. If it tastes too sweet at this stage, add a little more lemon juice; if it tastes too sharp even accounting for the dulling effect of freezing, add a tablespoon more sugar dissolved in a splash of warm water. Pour the mixture into a shallow, freezer-safe container — a metal baking tin or a wide, flat plastic container both work well; the shallower and wider the container, the faster and more evenly the sorbet freezes. Cover and freeze for 2–3 hours until the sorbet is frozen around the edges and semi-solid in the centre, with a slushy consistency throughout.

Remove the semi-frozen sorbet from the freezer. It should look like a thick, icy slush — frozen at the edges and slushy in the middle. Scrape the entire contents into a food processor or large bowl. If using a food processor, blitz for 30–40 seconds until smooth and creamy. If using a bowl, beat vigorously with an electric hand whisk for 1–2 minutes until the icy crystals are broken down and the mixture is smooth and slightly increased in volume. Add the lightly beaten egg white and beat or blitz again for 30 seconds until fully incorporated — the egg white introduces tiny air bubbles that give the sorbet its silky, scoopable texture and prevent it from freezing into a solid, icy block. Pour the beaten sorbet back into the container, cover, and return to the freezer for a further 3–4 hours, or overnight, until completely firm and scoopable. If you have an ice cream machine, churn the cooled lemon syrup mixture in the machine according to the manufacturer's instructions, adding the egg white in the final 2 minutes of churning, then transfer to a container and freeze for 1 hour to firm up.

Remove the sorbet from the freezer 5 minutes before serving to soften slightly — a sorbet that is too hard straight from the freezer is difficult to scoop cleanly and the flavour is muted by the extreme cold. Remove the frozen lemon shells from the freezer. Using a dessert spoon or small ice cream scoop, scoop generous balls of sorbet into each frozen lemon shell, mounding it slightly above the rim of the shell. Work quickly — the shells will begin to frost and the sorbet will begin to soften. Tuck a small sprig of fresh mint into the sorbet in each shell. Serve immediately on chilled plates or a chilled platter. If you need to prepare ahead, fill the shells with sorbet and return them to the freezer on a tray for up to 2 hours before serving — remove 5 minutes before serving to soften slightly. The sorbet keeps in the freezer for up to 2 weeks; after that the texture begins to deteriorate and ice crystals form.