- ½ cup granulated sugar
- 4 egg yolks
- Optional: 1 tsp cornstarch or potato starch
- 1¾ cup boiling milk
- 1 Tb vanilla extract
- OR, 1 tsp vanilla extract and 1 Tb rum, kirsch, cognac, orange liqueur, or instant coffee
- OR, 2 or 3 ounces or squares of semisweet baking chocolate melted in the boiling milk, and 1 tsp vanilla extract stirred into the finished sauce
- A 3-quart mixing bowl
- A wire whip or electric beater
- A clean, heavy-bottomed enameled or stainless steel saucepan
- A wooden spatula or spoon
- Optional but recommended: a candy thermometer
- Gradually beat the sugar into the egg yolks and continue beating for 2 to 3 minutes until the mixture is pale yellow and forms the ribbon.
- Beat in the optional starch.
- While beating the yolk mixture, very gradually pour on the boiling milk in a thin stream of droplets so that the yolks are slowly warmed.
- Pour the mixture into the saucepan and set over moderate heat, stirring slowly and continuously with a wooden spatula or spoon, and reaching all over the bottom and sides of the pan, until the sauce thickens just enough to coat the spoon with a light, creamy layer. Do not let the custard come anywhere near the simmer. Maximum temperature is 165 degrees on the candy thermometer (170 if you have used starch). Then beat the sauce off heat for a minute or two to cool it. Strain it through a fine sieve, and beat in one of the flavorings.
- To serve hot: Keep the sauce over warm but not hot water. If you wish, beat in 1 to 2 tablespoons of unsalted butter just before serving.
- To serve cold: Set the saucepan in a pan of cold water, and stir frequently until cool. Then cover and chill.