This is the Mexican version of Eggnog, served during the holidays.
1 14-ounce can sweetened condensed milk
2 cans (28 ounces) water
1 Mexican vanilla bean, sliced open
5 egg yolks
1/4 cup grain alcohol (or vodka, rum or brandy), or to taste
Using a wooden spoon, mix the milk and water in a small saucepan over medium-high heat until it boils. Reduce heat and add the vanilla bean. Simmer for about 5 minutes, stirring occasionally. Let it cool completely.
When cool, stir the egg yolks and strain them into the milk mixture. Return the saucepan to low heat, stirring constantly with the wooden spoon, until the mixture begins to boil. (Some of the mixture will stick to the wooden spoon at this point, which is another indication that it is done.) Remove from heat and let it cool.
When the mixture is completely cool, gradually add the alcohol, stirring constantly. Strain the mixture into clean bottles and refrigerate. Rompope can be kept in the refrigerator for about six months.