"Real Good"Potato Soup

Double Batch  (The Big Batch.  Need large Kettle.)
5 lb bag of potatoes
½ cup butter (full stick)
1 cup flour
1 gallon milk
2 Big onions
3 cup cheddar cheese, shredded
2 cups sour cream (1 container)
3 tsp. salt
1 tsp. pepper
Peel potatoes and chop into small pieces.  Melt butter in large pot and slowly stir in flour.  Whisk milk and bring to almost boiling over medium heat.  Add potatoes and onions, stir in cheese and sour cream.  Heat throughly until cheese is melted and soup is warm.  Garnish with chopped green onions and crumbled bacon if desired.