If you've ever encounter a recipe that told you to, "Bake in a hot water bath" with no further instruction, keep reading.
Some ingredients are just more sensitive than others, and as you discover more about food, you learn how to handle even the most delicate of ingredients (talking about you, meringue). One of the most essential tools in that category is the hot water bath, sometime called a bain-marie. Used most often for egg-based custards, a hot water bath cooks foods surrounded by water, helping to protect against the harsh heat of the oven which can lead to overcooked and gummy custards.
Preparing a hot water bath is simple: place your individual-sized or full-sized baking dishes in a container that's slightly larger. Pour in hot water, and you officially have a hot water bath!
Setting up the pan
Choose a pan large enough to comfortably hold the egg dish to be baked. There should be enough room for water to be poured halfway up the sides of the dish and circulate around the dish to act as a buffer from the oven’s heat. You can also elevate the dish to prevent direct contact with the bottom of the pan, using a wire rack for a single large dish or a folded kitchen towel for custard cups or soufflé dishes, which might shift on a rack.
Filling the pan with hot water
Position an oven rack in the center of the oven and pull it out only halfway, so that it doesn’t tip as you fill the pan. Set the baking pan with the filled custard dishes on the rack.
Carefully pour the hot water into the pan so that it comes one-half (or at least one-third) of the way up the side of the dishes. Push the rack carefully back into the oven. Check the pan periodically. If the water is boiling, lower the oven temperature slightly and replace the water that boiled away.
Removing the dishes
When the custard is properly baked, carefully pull the oven rack out halfway. Using an oven mitt or tongs, lift the dish(es) out of the bath and set on a wire rack. Leave the water-filled pan in the oven until it cools.