The "traditional" proportions for this dessert is one whole egg to every five egg yolks for 2 1/2 to 3 cups of liquid. A dessert made with these basic proportions will yield a barely firm custard. This is why the custard is best served in small pots (or ramekins). The earliest documented version of this dessert we could find was cooked and chilled prior to serving in the little cups. Today it is common from the custard to be baked in the little cups, in a water bath.
The method most common method today is as follows. Milk, heavy cream or half and half is heated and the flavoring (commonly chocolate) is melted after the liquid is removed from the burner. The eggs are whisked until smooth. Then, the hot flavoring mixture is gently whisked into the eggs.
The custard is then strained through a fine sieve to remove any bits of egg or chocolate not properly incorporated. This is a very important step to avoid any unpleasant bits of egg that might ruin the smooth texture of the dessert. We strain the mixture into a large measuring cup. This makes it easy to pour the custard into the little cups.
The cups are filled ¾ full with the custard mixture then placed in a baking dish. Hot water is added to the pan so that comes up at least 1/2 way up the sides of the cups. The image below was taken before all the water was added. Make sure it goes half way up the sides of the dishes you are using. If you are using pot de creme cups we don't suggest you use the pot de creme lids at this point. Simply cover the whole pan with a sheet of aluminum foil. The foil promotes even heating and prevents a "skin" from forming on the top of the custard.
The custard is placed in the preheated oven and baked in the bath of hot water. This process allows the eggs to cook slowly and evenly. The custard is baked in a low to moderate oven for about 20 minutes (this time will vary depending on the recipe). It's important not to overcook the eggs because they will get "rubbery".