Orange Ice Cream

Finely grate 2 tablespoons zest from oranges, then halve oranges and squeeze enough juice to measure 1/2 cup. Discard oranges.
Bring milk, 1/4 cup sugar, a pinch of salt, and 1 tablespoon zest to a boil in a 2-quart heavy saucepan, then remove from heat and let steep 30 minutes.
Beat together yolks and remaining 1/4 cup sugar in a medium bowl with an electric mixer until thick and pale, about 1 minute. Add milk mixture in a stream, whisking constantly until combined well. Pour mixture into same saucepan and cook over moderate heat, stirring constantly with a wooden spoon, until mixture coats back of spoon and registers 175°F on thermometer (do not let boil). Immediately remove from heat and pour through a fine-mesh sieve into a metal bowl. Set bowl in a larger bowl of ice water and stir until cold, 10 to 15 minutes.
Stir in orange juice and remaining tablespoon zest and freeze in ice cream maker. Transfer ice cream to an airtight container and put in freezer to harden, at least 2 hours.