Peel and chop the potatoes and set aside. In a large soup pot heat 2 tbsp of vegetable oil and add the onions, garlic, cumin, and annatto. Cook until the onions are soft, and then add the potatoes. Mix in the potatoes so that they are covered with the sofrito. Then, add the four cups of water and three cups of chicken stock and bring to a boil. Cook until the potatoes are tender. Once tender, mash them with a potato masher. Lower the mixture to a simmer and add the milk to thin out the soup slightly. Add the salt and pepper to taste as well as the 1 cup of the Queso Ecuatoriano and most of the cilantro. Leave some for a garnish at the end. Stir in the cheese and cilantro until the cheese has melted and the cilantro has mixed in. Remove from the heat.
Serve the soup and garnish with sliced avocados, the remaining crumbled Queso Ecuatoriano and cilantro.