Blend or process lucumas with milk until a thick purée is obtained. Force through a strainer.
Place evaporated and condensed milk in a heavy bottom pan with sugar and bring to a boil, stirring constantly until mixture thickens and the bottom of the pan can be seen.
Add lúcuma purée and continue cooking until mixture thickens again. Add vanilla.
Remove from fire and add yolks, slightly beaten. Return to medium heat for 3 minutes, always stirring. Mixture must not boil. Remove from heat and transfer to a bowl. Set aside until almost cool.
Beat whites until thick. Gradually fold into milk mixture, carefully.
Transfer to a serving bowl. Sprinkle cinnamon on top and refrigerate.
Fresh lucuma substitution:
2 pounds of fresh lucuma = 4 tablespoons dehydrated lucuma powder.
Soak lucuma powder in the same quantity of liquid 2 or 3 hours before using it. Stir. It will have the consistency of a puree.