A DOUBLE boiler is a piece of kitchen equipment consisting of two different sized sauce pans. Water is placed in the larger base pot. A second pan sits above and inside the bottom pot, surrounded by the water. The double boiler is used for cooking ingredients requiring the gentlest of heat. Simmering (not boiling) water surrounds the base of the upper pot, gently warming delicate sauces and custards, melting chocolate or cooking eggs. The water diffuses the heat from the range, giving greater control of the internal pot's temperature. The top pot can be lifted out, removing it from any ongoing heat source.

There are dozens of different double boilers available. Though their basic designs are similar, materials used for constructin range from enamel over sheet steel to tinned copper and porcelain. The classic tin-lined French copper double boiler with porcelain insert is my favorite example for illustrating that in terms of function you don't always get what you pay for. Their pots sell for about $65. You pay that whopping price for a finely made, tin-lined, copper pan with sides that slant in from the base so swiftly the pot is virtually unusable as a sauce pan. The slant is essential to stabilize the weight of the extremely thick porcelain upper pot. There is a copper lid that sits atop this upper pot. It's expensive and its highly heat conductive material is totally useless. But the entire piece of equipment is utterly beautiful and in the end will perform as a double boiler.

The ultimate double boiler, in terms of function, is the Pyrex glass model. Actually two sauce pans, one fits inside the other, or they can be used separately. Since the reason for using a double boiler is to bring a gentle heat to delicate ingredients, it is helpful to be able to see through the glass and know exactly what's going on. You will know instantly whether the whether the water is at a proper simmer, a dangerous rolling boil, completely dead or evaporated. You can see if the chocolate is melted to its proper consistency or about to burn. Like the French porcelain insert, the Pyrex pot is nonporous and will not interact with any foods. The base pan has a 1 1/2 quart capacity. The top pot will hold 1 1/4 quarts, and there s a Pyrex lid that will fit either pan. At $19.95, a real bargain.

The most inexpensive of the functional double boilers available is made by General Housewards Corporation. It is constructed of steel, covered with porcelanized white enamel. The clear white, glass-like surface is ideal for controlling cleanliness. The inset pan has curved sides that are ideal for whisking. The lids fit both pans, and the handles have holes for hanging.

A combinatin double boiler and steamer is made in stainless steel by Farberware. There is a 3-quart saucepan bottom with an aluminum base for better heat conductin. A 2-quart upper bowl serves as the double boiler insert, and there is a second bowl that is perforated and serves as a steamer insert. There is also a lid. Suggested retail price is $29.95.

A wonderful little gadgewt I value highly is a 5-by-11-inch high metal trivet called, by its distributor, a Double Boiler Maker. Maker. It is a low cost aluminum tripod that will turn any two different sized saucepans or saucepan-and-saute pan combinations into a double boiler. Put the double boiler maker into the large pan. Set the smaller pan on top of the tripod. and fill the outside pan with enough water to surround the base and lower sides of the inner pan. Eureka! You've made a double boiler, and it can be as big or as small as your pot selection will allow. The upper surface of the double boiler maker has a series of ridges that keep the top pot from sliding. It is well constructed out of a single solid piece of aluminum and retails for $4. i

The Flame-Tamer uses the same heat regulation principle as a Thermopane window. Made by Tricolator in France it consists of a hollow steel disk that traps a 3/4 inch layer of air between the burner and the pot. You can use this as you would a double boiler, but bear in mind it only comes in contact with the bottom of the pot and not up the sides as does the warm liquid in a double boiler.