Broil poblano peppers 4 inches from the heat until skins blister, about 5 minutes. With tongs, rotate peppers a quarter turn. Broil and rotate until all sides are blistered and blackened. Immediately place poblanos in a small bowl; cover and let stand for 20 minutes.
Peel off and discard charred skins. Remove stems and seeds. Coarsely chop poblanos.
In a Dutch oven, brown beef in oil in batches. Remove and keep warm. In the same pan, saute onion until tender. Add garlic; cook 1 minute longer.
Gradually add broth; stir in the tomatoes, cilantro, chili powder, salt, cumin, pepper, poblanos and beef. Bring to a boil. Reduce heat; cover and simmer 1-1/2 hours or until beef is tender. Add potatoes; cook 10-15 minutes longer or until potatoes are tender. Skim fat.