La Herencia publisher Ana Pacheco says this is her favorite, no-fail, natillas recipe. We trust her.
Natillas (Boiled Custard)
1 pint milk 1/4 teaspoon salt 2 tablespoons flour 1 teaspoon vanilla 2 eggs 2/2 cup sugar
Beat yolks, add sugar, flour and salt. Add to hot milk and boil until it thickens. Add vanilla. Beat whites until stiff, fold in the natillas and sprinkle with powdered cinnamon. - "El Plato Sabroso Recipes," by Doqa Eloisa Delgado de Stewart