Place beans in a large Dutch oven; add water 2" above beans. Bring to a boil. Boil 2 minutes; cover, remove from heat, and let stand 1 hour. Drain; return beans to pan.
Cut peppers in half lengthwise; discard seeds and membranes. Place peppers, skin side up, on an aluminum foil-lined baking sheet, and flatten with palm of hand. Add whole tomatillos to baking sheet. Broil 5 1/2" from heat 15 to 20 minutes or until blistered and charred, turning tomatillos once.
Place peppers in a heavy-duty zip-top plastic bag; seal and let stand 10 minutes to loosen skins. Peel peppers; coarsely chop peppers and tomatillos.
Meanwhile, cut off pointed end of garlic; place garlic on a piece of aluminum foil, and drizzle with 1 tablespoon oil. Fold foil to seal. Bake at 425° for 30 minutes; cool. Squeeze pulp from garlic cloves; set aside.
Sauté onion in remaining 1 tablespoon hot oil until tender; add to beans. Add peppers, tomatillos, chicken broth, and next 4 ingredients. Bring to a boil; cover, reduce heat, and simmer 1 hour and 45 minutes or just until beans are tender. Stir in cilantro and roasted garlic. Simmer 10 more minutes. Ladle chili into bowls; top with sour cream and croutons.