In a large stock pot, cook bacon until crisp. Remove with a slotted spoon to drain and set aside. Drain all but 2 tablespoons of bacon grease from the pot. Cook the onions in the remaining bacon grease for about 5 minutes, until tender.

Add potatoes and chicken stock to pot. Bring to boil, reduce heat to medium and simmer about 20 minutes, until potatoes are tender. With a slotted spoon, remove a few scoops of potatoes. Place in a bowl and mash with a fork. Set aside.

In a small sauce pan, melt butter. Stir in flour and cook for 2 minutes. Whisk in milk, bring to boil and simmer until thickened. Slowly stir into stock pot. Bring to a boil, reduce heat to low and simmer. Stir mashed potatoes back into pot.

Add 1/2 cup shredded cheese, three-fourths of the bacon and half the sliced green onions to the pot. Add pepper. Stir to combine. Cook an additional 5 minutes.

To serve, ladle soup into individual bowls and top with some shredded cheese, bacon, green onions and optional sour cream.