In which scenario would you need to use a water bath when baking?

Using a water bath, also known as a bain-marie, is essential when baking custards because it helps maintain a gentle and even cooking temperature. Custards are delicate mixtures that can easily curdle or become grainy if exposed to direct heat. By placing the custard dish in a water bath, the surrounding water provides a buffer against high temperatures, allowing the custard to cook slowly and uniformly. This method helps achieve a silky texture and prevents overcooking, ensuring that the custard sets properly without becoming lumpy.

In contrast, other options may not necessitate this technique. Meringues rely on the incorporation of air and are best baked at higher temperatures for a crisp exterior. Chocolate cakes typically tolerate direct heat and can be baked reliably without a water bath. Bread baking usually requires dry heat for optimal crust formation and development, which would be inhibited by steaming from a water bath. Therefore, the need for a water bath is particularly crucial in scenarios such as making custards to ensure they achieve the desirable consistency and flavor.