Pour the sugar into a pot. Zest the lemons over it and then rub the zest into the sugar with your fingers, this releases the natural oils in the zest. Add the salt, heavy cream, milk and egg yolks and whisk well to combine.

Set the pot over low heat and cook until slightly thickened and a thermometer registers 160F. Off the heat, add the lemon juice and the vanilla and whisk to combine. Pour the mixture through a fine mesh sieve into a heatproof bowl. Leave it on the counter until it comes to room temperature, then cover it to seal and set in the fridge for at least 8 hours but ideally overnight.

After the chill period, the ice cream base will have likely developed a thick layer on top, whisk it to make it smooth. Churn the ice cream according to the machine’s instructions. Store in a freezer safe container. Ice cream will be good to eat for 2-3 weeks.