Here is what I found when googling the subject. I have a clay baker
(not Romertopf) and the inside of the bottom portion is glazed. I
might try baking bread in it w/o the oiling and see what happens.
One Perfect Loaf
1 cup warm water (105-115 F)
1 package active dry yeast
1 teaspoon sugar
3/4 tablespoon salt
1 tablespoon vegetable oil
3 cups (approx.) all purpose flour
Baking bread in a wet clay cooker results in a crisp shiny crust you
may have thought possible only in a baker's brick oven.
Place warm water in a large mixer bowl and sprinkle with yeast.
Let stand until softened, about 3 minutes.
Stir in sugar, salt and oil.
Add 2 cups of the flour.
Mix until blended; beat on medium speed until dough is elastic and
pulls away from bowl, about 5 minutes.
Stir in 1/2 cup of the flour to make soft dough.
Turn dough onto floured surface.
Knead, adding flour as needed, until dough is smooth and springy and
small bubbles form just under the surface, 15 to 20 minutes.
Place dough in greased bowl; turn greased side up.
Let stand covered in warm place until doubled, about 1 hour.
Soak Romertopf bottom of loaf shaped, 5-1/2 cup clay cooker in water
about 15 minutes.
When dough has doubled, drain bottom of cooker pat dry.
Grease sides and bottom generously.
Punch dough; shape into loaf and place in cooker.
Let stand, covered with waxed paper, in warm place until dough nearly
reaches top of cooker, 30 to 45 minutes.
Cut diagonal slashes, 1/2 inch deep, in top of dough with razor blade
or sharp knife.
Soak top of cooker in water about 15 minutes; drain; pat dry and grease.
Place covered cooker in cold oven.
Set oven at 475 F.
Bake 45 minutes.
Remove cover, bake until top is brown, 3 to 5 minutes.
Remove from cooker and cool on wire rack.
The above recipes are from Clay Cookery by the editors of Consumer Guide
Sonia R. Martinez
Cookbook author and freelance food writer