Preheat oven to 400 degrees F. Pierce potatoes with a fork; bake for one hour or until potatoes are tender. Let the potatoes cool. Peel potatoes and coarsely mash them in a small bowl. Set aside.

In a large soup pot, add the flour. Gradually whisk in the milk, whisk until smooth. Cook over medium heat until thick, about 8 minutes. Add mashed potatoes, cheese, salt, and pepper. Stir until the cheese melts.

Add in sour cream and green onions. Cook over low heat until thoroughly heated, do not boil the soup. Ladle soup into bowls and garnish with toppings. Serve warm.