One of the earliest ways to bake bread was underneath a curved cover
or cooking pot placed over an open hearth. This is such a cooking
bell made from hard-fired clay that nests on a lipped baking stone
10-in. diameter.
Place your bread dough on the pie-shaped base, cover it with the
bell, then put it in a preheated oven.
A 2-pound loaf fits under the 6-in. high dome. The lid traps moisture
escaping from the bread to create the steam needed to produce a
light, brittle crust. During the last few minutes, remove the cover
to lightly brown the crust.
This information below comes from "Brother Juniper's Bread Book" by
Peter Reinhart, page 165. This was one of his earlier books.
"If you decide to try baking with a cloche, spray the dome thoroughly
with water before putting it in the oven. The round dome calls for a
round loaf and the final rise is done right on the clay plate. Be
sure that there is ample polenta (corn meal) under the loaf to
prevent the dough from sticking. Because the dome keeps heat out as
well as in, turn the oven up to 450 F. When the dough is 3/4
proofed, spray it, spray the lid and slash the loaf. Put in the oven
with the lid on. After 5 min. lower the oven to 425 F. The loaf
will take longer to bake than uncovered loaves, about 1 hr. When it
appears to be done remove the dome, turn off the heat, and give the
bread a 10 min cool down in the oven."