The secret to a perfect Rompope is to add the liquor of your choice before serving.
The first rompope, a derivation of Spanish ponche de huevo (egg punch), was brewed by seventeenth-century nuns in the Santa Clara convent in Puebla, Mexico. According to legend, Sister Eduviges requested that the nuns be allowed to drink the rompope that only they were permitted to make. Legend also has it that there was one secret ingredient in the recipe that Eduviges took with her to the grave.
Fortunately, this Rompope recipe has been handed down through the ages. It's served chilled, often over ice, but can also be served warm, which is how I prefer it when the cold weather sets in. Either way, it's rich, velvety, fragrant, and full of cheer.
2/3 cup almonds sliced
1 1/2 cups brown sugar plus 2 tablespoons, divided
Pulse almonds with 2 tablespoons of the sugar in a food processor until ground to a fine paste.
Bring milk, cinnamon, vanilla, and baking soda to a boil over medium-high heat in a large heavy-bottom saucepan. Reduce heat to medium-low and simmer for 15 to 20 minutes. Set aside.
In a large bowl, whisk egg yolks, the remaining 1 1/2 cups sugar, and ground almonds until thick and pale.
Add the sugar and yolk mixture to to the saucepan and whisk constantly.
Cook over low heat, continuously stirring and scraping the bottom and sides of the pan, until the mixture thickens enough to coat the back of a spoon, 5 to 7 minutes. Set aside to cool completely, about 1 hour.