* First human beings created fire. There was great rejoicing. Then human beings discovered that the same flames that warmed the hands also curdled the cre me anglaise. And that wouldn't do.
So ever since that moment, human beings have tried to figure out a way to moderate the fire, to get the flames to cook but not burn.
The French were the most concerned about this problem, so they invented the bain-marie or water bath method of protecting sensitive foods from the fire. (You heat the water directly over the fire and the water heats the food. Water always has a moderating effect on temperature.)
Soon every bride in America found a Revere Ware double boiler, which would in some cases be with her longer than her spouse, among her wedding presents. Everybody has -- or had, before American social convention began decreeing woks and pasta makers instead -- a Revere Ware double boiler. And it's just fine.
A bain-marie is, technically speaking, a slightly different proposition. With the double boiler you heat the food over but not in the hot water, while in the bain-marie you put the food (contained, of course) in the water. But the goal, to protect the food from the fire, is essentially the same.
A Flame-Tamer, which is a perforated metal disk that you put on the burner, has a similar effect. But water is the gentlest influence of all, and it's water you want between your flame and your tender sauces, sensitive custards and melting chocolates. Eggy custards, mousses and timbales, for example, are always laid gently into a bath of very hot water before being put into the oven. And professionals even put several layers of paper towels between the bottom of the water container and the bottoms of the custard cups, for added protection.
No special equipment, not even the Revere Ware double boiler, is absolutely indispensable for top-of-the-stove cooking. Lots of cooks, including professionals, prefer to improvise. Even for large amounts you can always just put a big bowl in a big saute' pan full of water and keep the heat low. And if you make cre me anglaise ("boiled" custard) often, you already know that in the half-hour it takes to thicken it in a double boiler you could have done all kinds of fun other things.
But there are two contraptions that you might want to consider anyhow, because they do take most of the fear and trembling out of doing this kind of cooking.
One is the classic French double boiler, which consists of a copper saucepan with a thick white ceramic insert. In good-quality sets the lower portion is usually lined in tin and the top fits both the ceramic insert and the saucepan. In other words, you should be able to use the saucepan independently.
The ceramic insert provides terrific insulation; it's very difficult to overheat even the most tender sauces in this material. Scrambled eggs will be creamy and soft, even large quantities of chocolate will melt evenly, the lemon pie filling will thicken without scorching and the cre me anglaise will be perfectly smooth.
Of course this last will take practically forever and there won't be any thrill (will it curdle? won't it curdle?) but the custard will be perfect, almost certainly. An advantage, on the other hand, of this leisurely pace is that you have a longer window of time at the end of cooking to determine the perfect moment to take the stuff off the heat. Working with direct heat, the window is only open for a few seconds.
If you go shopping for such a double boiler, look for the quality of the copper bottom part; along with how well the top fits, this will determine how much you'll be able to use it separately. These double boilers will cost somewhere between $75 and $100 depending on their size and the store in which you buy them. They are extravagant but they are beautiful.
Not so beautiful but efficacious along the same lines is a German-made product called the Simmerpot. This looks something like a stainless steel pitcher without a spout. In fact there are two layers of stainless steel, and between them goes a cup or so of water. When you heat the pot on the stove top the water partially surrounds and protects the inner contents of the pot from too much heat.
On a low flame the temperature of the pot's contents stays just below the boiling point, making it perfect for all those sauces that shouldn't boil. This is not to say that it's impossible to overheat things in this pot; as with any other pot, if you let the custard cook too long it will curdle no matter how gentle the heat.
I found the Simmerpot ideal for the even melting of chocolate, especially large quantities; for reheating leftovers; and for making cre me anglaise and scrambled eggs. Cre me anglaise took about 25 minutes to complete, with stirring only from time to time. Chocolate melted more evenly than it usually does, and the cre me anglaise showed no signs of glopping up, even around the edges. The manufacturer touts the product for heating milk, which it will do without scorching or boiling over, but it takes a very long time compared with heating it directly.
The Simmerpot usually costs about $60, but it's been on sale recently at Williams-Sonoma for $48.