In a large stock pot, melt butter over medium heat. When the butter has melted, whisk in flour and allow the mixture to cook for a few minutes.
Slowly add in 7 cups of milk, 1 cup at a time, whisking really well between each cup.
When all 7 cups of milk have been added, continue whisking until the mixture starts to thicken a bit.
Add in cubed baked potatoes and green onions. Then bring to a boil making sure to stir frequently.
Reduce the heat to low, then stir in the cooked bacon, cheese, sour cream, salt and pepper.
Serve immediately once the cheese has melted. Garnish each bowl of soup with additional cheddar cheese, bacon crumbles, and chopped green onion.