Why Bread Needs Steam in the Oven

Heat starts the bake, but moisture matters too. During oven spring, steam helps the loaf's surface stay flexible so the dough can expand before the crust sets.

Add steam with a separate tray

1. Place a separate oven-safe metal steam tray on a lower rack, below the bread. Use a tray suitable for this purpose and your oven.
2. For this method, preheat the suitable metal tray with the oven.
3. As you load the loaf, carefully add hot water to the steam tray and close the oven door. Wear oven mitts and keep your face and hands clear of the rising steam.
4. Keep water off the oven glass and baking surface. Do not use a glass dish as a steam tray.
5. Once the initial rise is complete, finish in a dry oven so the crust can crisp. If removing the tray, handle it carefully with oven mitts and avoid spilling hot water.

What about a covered pot?

A covered pot traps moisture released by the dough. The lid supplies the enclosed steaming environment; an open bake uses the separate tray instead.

Steam early, then finish dry.

Further reading: King Arthur Baking: baking bread with steam.