Heat the oil in a large saucepan add the onions, scallions and garlic, cook on medium low heat for about 8 minutes, stirring occasionally.
Add the chicken, cumin, the broth and potatoes, bring to a boil.
Reduce temperature and simmer until the chicken is cooked and the potatoes are tender, about 30 minutes.
Season with salt and pepper, remove from the heat and let the soup cool until it is safe to blend.
Blend the soup, mix in the milk and cream, and reheat. Garnish with fresh cilantro or scallions and serve warm.