A thinner custard than the Westernized version, nai lao is a generations-old Chinese treat made with a few simple ingredients. Translated as "imperial custard," this cold dessert soup is prized in and around Beijing, but is fairly obscure to foreigners. What makes it distinct is the acidic tone that is created by adding rice wine to the custard's simple cream, which is sweetened only slightly by some sugar. A garnishing of nuts and raisins add texture at serving time.
Traditionally, nai lao custard is baked in tiny wooden yogurt barrels heated over hot coals. Other chefs employ a steam bath method or merely use an oven set to a low temperature until the custard takes on a thicker consistency. The key to making it correctly is striking the proper balance of sweet, full-cream milk and the rice wine. When done correctly, very little extra sugar should be needed.
The process of making nai lao begins by heating milk over low heat until it is just about to boil, which removes much of the bacteria. Chefs typically use a large pan on the stove for this part of the preparation. If cream is used, no sugar should be needed. When whole milk is used, many stir in some sugar during the heating. Covered and allowed to cool, the cream is then poured through a sieve to remove any impurities.
The rice wine is combined with the cream just before going into the oven or barrel at about 200°F (or about 90°C). Many use about one part wine for three parts of cream, whisking it into the milk slowly, until it is slightly frothy. In about a half-hour, the custard should be thickened to a creamy consistency with an off-white color. Some bake the custard bowls longer at a lower temperature to better combine the flavors.
The nai lao does not bake all together in a bowl, since the consistency would not be uniform. Instead, small oven-safe custard ramekins are used, one for each person to be served. Some raisins are thrown into the bottom of each ramekin, along with a few varieties of chopped nuts, like sunflower seeds or walnuts. Then, the nai lao is poured over the top, leaving a small lip at the top of the ramekin for the custard to expand.
If a barrel is used, the ramekins are stacked inside once the container has reached the right temperature. When cooking in an oven, the middle racks should be used to help the final product take on an even consistency. The treat is officially ready after a short cooling in the refrigerator.