It's not just bean pots, of course, for cooking with clay. Tagines, comales and cazuelas all work on a direct flame. This Mexican cazuela is from my pal Chris and it has somewhat high sides, so there's not as much evaporation as there would be on a broader one.
A nice feature, aside from the gentle cooking and rustic good looks, is the handles stay cool for quite a while.
I recently made a chile sauce in the cazuela. I soaked some anchos and New Mexican chiles in hot water for about 20 minutes and then added them, along with 1 small onion and 4 cloves of garlic, to a blender with enough of the soaking water to keep the blades moving. Then I added a spoonful of lard to the preheated cazuela and "fried" the sauce until it was reduced to a thick consistency, almost like tomato paste.
After about 10 minutes of constant stirring, I added about a cup of pureed tomatoes and a ladle full of turkey stock I had handy. I threw in some Mexican oregano for good measure. Stirring occasionally, this cooked for 20 minutes on a gentle simmer. Once the fat starts rising and shimmering, you're close to being done. Salt to taste.
This would be a great sauce for enchiladas or you could thin it out a bit with water or stock and gently poach a cut up chicken in it.