Special equipment: an ice-cream maker and a candy or instant-read thermometer
Directions
Bring cream, milk, sugar, zest, and salt just to a boil in a 2-quart heavy saucepan, stirring occasionally. Lightly beat yolks in a large bowl, then add hot sweetened cream in a slow stream, whisking. Pour custard into saucepan and cook over moderately low heat, stirring constantly with a wooden spoon, until a candy or instant-read thermometer registers 170°F and custard coats back of spoon, about 10 minutes. Pour through a sieve into a clean bowl, then stir in juice. Cool custard, stirring occasionally, then chill until cold.
Freeze custard in ice-cream maker. Transfer ice cream to an airtight container and put in freezer to harden.
Blend together preserves and lemon juice in a food processor until smooth. Strain sauce and/or thin with water if desired.
