A well-chilled custard base for a faster freeze
Other than the innovations mentioned above, these ice creams follow the same method as most others: make a custard base, cook it until it thickens, chill it, and spin it in an ice-cream machine until frozen.
Cooking the base does two things: it heats the milk (essential for a smooth texture), and it eradicates any concerns about salmonella in the eggs (the bacteria can’t survive above 160°F). To avoid overcooking the custard, take the following precautions:
• Add the milk to the egg yolks gradually. Adding eggs abruptly to a very hot mixture can cause them to curdle. To increase their temperature gradually, whisk a bit of the hot liquid into the yolks before mixing them into the rest of the hot mixture, a process called tempering.
• When the custard is ready, stop the cooking. As the custard nears 180°F, it begins to thicken very quickly. To halt the cooking, remove the pot from the heat and mix in the remaining ingredients, which should be chilled.
You could set up an ice bath to cool the custard even faster, but it’s an extra step that’s easily omitted. Even if a few specks of cooked egg are in the custard, it isn’t the end of the world: you’ll be straining the mixture before chilling it.
I’ve had great results by refrigerating the custard base for as little as two hours or for as long as 24 hours before pouring it into an ice-cream machine. Just keep in mind that the colder the base is, the quicker and easier it will freeze.