How to Make It
Add 1 generous tablespoons of condensed milk into a tall, 12-ounce glass or larger. Add 1 large egg yolk or 2 small yolks. Pour club soda into glass, stirring quickly until yolk, condensed milk and soda water are evenly mixed and at least a 1/2 inch of froth appears at the top of the glass. Pour over ice and serve.
For a more eggnog-like flavor, add a couple drops of vanilla extract, stir, then sprinkle with cinnamon and nutmeg powder.