If you have ever seen a cracked cheesecake or eaten a rubbery custard, chances are that they were baked without using the help of a water bath. A water bath or bain marie is a technique used to prepare foods that require more moisture while baking. Basically, custards, terrines, and other delicate dishes and baked in a pan filled with hot water. The water provides a constant, steady heat source and ensures even cooking.
The best way to prepare a water bath is to warm the water on the stove top in a tea kettle. Line a roasting pan or other high-sided baking dish with your least favorite kitchen towel and place your filled spring form pan, ramekins or loaf pan. If your recipe specifically calls for a springform pan, wrap the pan first with aluminum foil to prevent water from leaking through the bottom. Bring the pan to the oven and place it on the middle rack with the rack extended. The rack should be steady and secure before the water is added. Carefully pour the hot water (without splashing) into the pan until it has reached half way up the sides. You can also add the water before moving the pan to the oven but then you will have to worry about the water spilling into your dish. This is especially true with small ramekins.
While your dish is cooking, keep an eye on the water to make sure it is not anything over a subtle simmer. If the water is boiling, the oven it too hot and your finished product will more than likely be overcooked. When removing the pan from the pan from the oven, exercise the same caution you did when putting it in.