Add onions, celery, garlic, oregano, cumin, coriander and cayenne and saute until onions are transparent. Whisk in flour and cook for one minute.
Whisk in broth and potatoes and turn heat up to medium high and bring to a boil. Boil potatoes until they are fork-tender (about 15 minutes).
Reduce heat to low and with a potato masher, mash potatoes in the pot to desired consistency. Stir in evaporated milk and cheese until cheese is melted.
Remove pot from stove and stir in sour cream, salt and pepper. Serve warm.