To prepare the custard cream, in a medium-size saucepan bring the milk and cream short of a boil over medium heat.

In a large bowl or in the top of a double boiler off the heat, beat the egg yolks and sugar together with an electric mixer at high speed until pale yellow and thick.

Pour the milk very slowly into the eggs, beating constantly with a wire whisk until all the milk has been added. Set the bowl or top of the double boiler over simmering water and cook, whisking constantly, until the cream coats the back of a spoon evenly, 6 to 8 minutes. (Do not let the cream boil as it cooks or it will curdle the eggs.) Cool the custard completely to room temperature.

In a large bowl, combine the custard cream with the heavy cream and set aside.

In a small skillet, combine the lemon juice with the sugar and zest. Cook over medium heat, stirring, until reduced by about half. Cool to room temperature.
Stir the sugar mixture into the custard cream and place in the bowl of a chilled ice cream machine. Run the machine for 15 to 20 minutes. Transfer the ice cream to a plastic container and freeze for several hours or until you are ready to use it.