In a small heavy saucepan, heat milk to 175°; stir in sugar until dissolved. Whisk a small amount of hot mixture into egg yolks. Return all to the pan, whisking constantly. Add lemon zest. Cook over low heat until mixture is just thick enough to coat a metal spoon and a thermometer reads at least 160°, stirring constantly. Do not allow to boil. , Remove immediately from heat; stir in lemon juice and cream. Place in a bowl. Press plastic wrap onto surface of custard; refrigerate several hours or overnight., Fill cylinder of ice cream freezer two-thirds full; freeze according to the manufacturer’s directions. (Refrigerate remaining mixture until ready to freeze.) Transfer ice cream to freezer containers, allowing headspace for expansion. Freeze 2-4 hours or until firm. Repeat with remaining mixture.