Stick an airtight freezer-safe quart container in the freezer. Combine the cream, milk, vanilla, and salt in a medium saucepan set over medium heat. Heat until steamy, 5 to 7 minutes, scraping the bottom of the pot regularly with a flexible spatula to prevent any sticking or burning.
Meanwhile, whisk the egg yolks with the sugar in a medium heat-proof mixing bowl until smooth.
When the cream mixture is steaming, slowly whisk it into the egg mixture. (Pour too quickly, and you’ll get scrambled eggs.) Add the combined custard back to the pan (reserving the bowl), and set over medium-low heat. Cook to 180°F, again scraping the bottom regularly to prevent any sticking or burning. If you don’t have a thermometer, dip a spoon in, and draw a line through the custard with your finger. If the custard is thick enough to hold that line cleanly, it is ready.
When the custard is ready, pour it back into the mixing bowl, and set into a larger bowl or sink filled with ice water. Stir occasionally until chilled to room temperature, about 20 minutes, then stick in the fridge for another hour. (The colder it is going into the ice cream machine, the better-textured!) Alternatively, skip the ice bath and let custard rest, covered, in the fridge for at least 4 hours.
When ready to churn, fine-strain the custard into an ice cream machine. Churn until frozen, about 20 minutes, or as instructed by the manufacturer. Transfer the ice cream to your chilled container, and cover surface with a parchment circle. Freeze until solid, about 2 hours, and keep in the freezer for up to 2 weeks.