Heat oven to 450F degrees and bake the potatoes until fork tender (1 hour).
Brown bacon in large heavy pot. Remove the pan from heat. Remove bacon from pan and remove half the fat.
Press the roasted potatoes through a potato ricer into the pot. Add milk and return to a low heat. Soup will thicken after about 10 minutes. Cook for at least another 5 minutes after the thickening begins. Add chicken stock to thin to desired consistency.
Whisk well, add sour cream and half the cooked bacon. Heat thoroughly. Season with salt and freshly cracked black pepper. Add cheese a little at a time until all is melted in. Stir in green onions. Serve. Top with crumbled bacon.