Make sure that the bowl of your ice cream maker has been in the freezer long enough to be fully frozen, ideally 24 hours.
Place the cornflour in a saucepan and gradually whisk in the milk to make a smooth paste.
25 g (2 ½ packed Tablespoons) cornflour (cornstarch), 250 ml (1 cup) unsweetened non-dairy milk (I use soy)
Whisk in half of the cream and the sugar.
500 ml (2 cups) vegan double (heavy) cream, 180 g (¾ cup + 2 ½ Tablespoons) caster or granulated sugar
Place the pan over a medium heat and stir constantly until it comes up to the boil and thickens to a custard consistency.
Pour into a large jug and whisk in the rest of the cream, the lime juice and zest and salt. Start with 120ml (½ cup) of lime juice and add more to taste.
finely grated zest 3 limes, 120-150 ml (½ cup to ½ + ⅛ cup) freshly squeezed lime juice (4-5 limes), ¼ teaspoon salt
Cover the jug and refrigerate until completely cold, at least 4 hours, I leave it overnight.
Once the ice cream mixture is thoroughly chilled, give it a good whisk then pour it into your ice cream maker and churn until it reaches soft serve consistency.
Transfer to a freezer-proof container and freeze for about 4 hours until firm. Once fully frozen the ice cream will be quite solid straight out the freezer, let it warm up at room temperature for fifteen minutes before scooping.