This gelato can be made without an ice-cream machine. Place the mixture in a shallow non-reactive metallic container in the coldest part of the freezer until the mixture freezes around the edges. Remove from the freezer and transfer to a chilled metallic bowl. Use an electric mixer to beat until smooth. Return to the same container and freeze until set.
1 litre (35 fl oz/4 cups) milk
Finely grated zest of 1 lemon
10 egg yolks, at room temperature
220 g (7 3/4 oz/1/2 cup) caster (superfine) sugar
125 ml (4 fl oz/1/2 cup) strained fresh lemon juice
1. Combine the milk and zest in a small saucepan and bring almost to the boil. Set aside for 10 minutes to infuse.
2. Use an electric mixer with a whisk attachment to whisk the egg yolks and sugar in a medium bowl until thick and pale. Whisk in the milk mixture until smooth.
3. Strain the mixture into a medium saucepan and then use a wooden spoon to stir over medium-low heat until the mixture coats the back of the spoon (do not let the mixture boil or it will curdle). Remove from the heat, cover the surface with plastic wrap and cool to room temperature. Refrigerate until cold. Stir in the lemon juice.
4. Pour the lemon custard into an ice-cream machine and churn following the manufacturer's instructions. Transfer the churned gelato to an airtight container and freeze for 2 hours or until firm.