Kaffir lime leaves may be a little difficult to procure—you can find them in specialty and Asian grocery stores—but their flavor and fragrance are inimitable and very much worth seeking out. This is a great ice cream flavor to pair with a Southeast Asian–themed menu. The leaves are often sold frozen, and it’s best to keep them that way until you are ready to use them. Stored properly, their shelf life can be extended far beyond that produced by mere refrigeration. Because the leaves can be tough and stringy, we recommend straining the custard after blending the leaves into it.
MAKES ABOUT 1 QUART
2 cups heavy cream
1 cup whole milk
½ cup plus 2 tablespoons (125 grams) sugar
¼ teaspoon (1 gram) kosher salt
6 large egg yolks
9 medium kaffir lime leaves (see Sources)
1. Pour the cream and milk into a double boiler or a heatproof bowl set over a saucepan of gently simmering water (the bottom of the bowl should not touch the water). Whisk in ½ cup (100 grams) of the sugar and the salt and stir until they have dissolved. Warm the mixture until you see steam rising from the top.
2. Meanwhile, prepare an ice bath in a large bowl and set another bowl over it. Set aside.
3. In a medium bowl, with a kitchen towel underneath it to prevent slipping, whisk together the egg yolks with the remaining 2 tablespoons (25 grams) sugar until uniform. While whisking, add a splash of the hot dairy mixture to the yolks. Continue to add the dairy mixture, whisking it in bit by bit, until you’ve added about half. Add the yolk mixture to the remaining dairy mixture in the double boiler. Set the heat under the double boiler to medium and cook the custard, stirring continuously with a wooden spoon and reducing the heat to medium-low as necessary, until steam begins to rise from the surface and the custard thickens enough to coat the back of the spoon. Hold the spoon horizontally and run your finger through the custard. If the trail left by your finger stays separated, the custard is ready to be cooled.
4. Strain the custard into the bowl sitting over the prepared ice bath and stir for 3 to 5 minutes, or until the custard has cooled. Transfer the cooled custard to a blender and add the kaffir lime leaves; blend until completely uniform. Strain the custard into a bowl to get rid of some of the kaffir lime leaf fibers. Transfer the custard to a quart-size container, cover, and refrigerate for at least 4 hours or, preferably, overnight.
5. Pour the chilled custard into an ice cream maker and freeze according to the manufacturer’s instructions. Place the container in which you refrigerated the custard in the freezer so you can use it to store the finished ice cream. Churn the ice cream until the texture resembles “soft serve.” Transfer the ice cream to the chilled storage container and freeze until hardened to your desired consistency. Alternatively, you can serve it immediately—it will be the consistency of gelato. The ice cream will keep, frozen, for up to 7 days.