Step 1

In a medium saucepan, pour 1 cup (250 ml) of the milk, all of the cream, and the lemon zest. Warm over medium heat until it just starts to bubble around the edge (no need to bring it to a boil).

Step 2

Meanwhile, in a small bowl, whisk the remaining 1 cup (250 ml) milk, sugar, and cornstarch together. Remove the saucepan with the hot milk from the heat and whisk in the cornstarch mixture. Return the saucepan to medium heat and cook, stirring regularly, until the sugar is dissolved, and the mixture thickens slightly, 6 to 8 minutes.

Step 3

Place the egg yolk in a medium bowl and whisk until pale and thickened, about 30 seconds. Temper the egg yolk by slowly pouring one ladleful of the hot milk mixture into the yolk, whisking constantly, then slowly pour the egg yolk mixture back into the saucepan, whisking to combine. Return to medium heat and cook, whisking constantly, for 1 minute more.

Step 4

Remove from the heat. Whisk in the freshly squeezed lemon juice. Cover the saucepan and let cool to room temperature.

Step 5

Once the lemon gelato custard is at room temperature, pour into an airtight container. Refrigerate for at least 6 hours, or preferably overnight. The lemon gelato base must be very cold before churning: this will produce the smoothest, silkiest texture.

Step 6

Strain the lemon gelato custard through a fine mesh strainer and discard the lemon zest.

Step 7

Pour the lemon gelato custard into the bowl of an ice cream maker and churn according to the manufacturer's instructions. Stop the machine when the lemon gelato is thick and icy but still easily spoonable.

Step 8

IF USING LEMON CURD: Spread one-third of the lemon gelato over the bottom of a storage container (I like to use a loaf bread pan to maximise the swirling effect). Cover with ½ cup (125 ml) of the lemon curd and use a knife to swirl it into the gelato. Cover another third of the lemon gelato, then another ½ cup (125 ml) of the lemon curd, swirling again. Finish with the remaining lemon gelato, spreading it to cover the lemon curd.

Step 9

OTHERWISE, simply transfer the lemon gelato to an airtight container and freeze until firm, about two hours.

Step 10

STORAGE: Lemon gelato is at its creamiest and best if enjoyed within 2 weeks. Past that, some ice crystals will inevitably start forming (especially if the gelato is kept in the freezer section of a regular fridge, as opposed to a chest freezer) and the texture won't be quite as smooth. The lemon gelato will still be perfectly edible for up to 2 months, but my advice is to enjoy it as quickly as possible after churning.

Step 11

SERVING: Always take lemon gelato out to room temperature 20 minutes before serving to make it easier to scoop. This will also allow you to enjoy the treat at its ideal temperature and texture.

Step 12

MAKE IT DAIRY FREE: Substitute lactose-free milk or oat milk for the regular milk, and lactose-free heavy cream or soy cream for the regular heavy cream.

Step 13

MAKE IT VEGAN: Substitute oat milk for the regular milk, and soy or coconut cream for the regular heavy cream. Get more tips for making vegan gelato.