1. In a large saucepan, mix the slightly beaten egg yolks, 3 cups of milk and sugar.
2. Put on a very small fire and, whisking, heat until the mixture thickens.
3. Remove from heat and slowly pour the remaining milk and add the grated zest.
4. Refrigerate, then freeze in ice cream maker, follow the instructions.
5. beforehand mass in portions of not more than 320 ml.