Stage 1 (10 minutes)
1. Puree the chipotles with the water in a blender and refrigerate.
2. Chop the onion, celery, and garlic. Put the onions, celery, and half of the garlic in one bowl and cover, Put the remaining garlic in a separate bowl and cover. Refrigerate both bowls.
3. Combine cumin and chili powder in a small bowl. Combine bay leaves, oregano, and 1 teaspoon salt in another small bowl. Measure cornmeal into a third bowl.
Stage 2 (10 minutes)
1. Heat the oil in a large, heavy pot or Dutch oven over medium heat. When it shimmers, add the onion mixture and cook, stirring occasionally, until softened, about 10 minutes.
2. Add the cumin and chili powder and cook, stirring, for 30 seconds.
3. Remove from heat; cool slightly, cover, and refrigerate.
Stage 3 (1½ hours, 30 minutes active)
1. Return the pot to the stove over low heat. When the mixture has warmed, increase heat to medium, add chicken, and cook, stirring, until chicken is no longer pink, about 8 minutes.
2. Add the chipotle puree, chopped tomatoes, broth, bay leaves, oregano, and salt, and simmer, uncovered, adding more water if necessary to keep the chicken barely covered, 1 hour.
3. Add the cornmeal and simmer, stirring occasionally, 15 minutes.
4. Stir in the white beans and remaining garlic and simmer until the beans are heated through, 3 to 5 minutes.
5. Adjust salt to taste, and discard bay leaves before serving over brown rice with cheese, sour cream, and chopped onion.