Heat oven to 400℉/200℃.
Wash and dry potatoes.
Prick all over with a fork.
Place potatoes on a rimmed baking sheet.
Bake for 1-1 ½ hours, until tender.
Set aside to cool.
Cut bacon into ½ inch pieces.
Sauté over medium heat until crisp.
Drain thoroughly. Set aside.
Peel potatoes.
Cut into 1-inch dice. Set aside.
In an 8 quart soup pot or dutch oven, melt butter over medium heat.
Whisk in flour until smooth.
Reduce heat to medium low and continue whisking for an additional 2 minutes.
Add milk, one cup at a time, whisking well after each addition.
Once all milk has been incorporated, add potatoes and cook, stirring occasionally, until mixture starts to thicken, about 5-10 minutes (depending on how your stovetop cooks).
Stir in bacon and green onions and cook for an additional 5 minutes.
Add cheese and stir until melted.
Stir in sour cream.
Heat through.
Season with salt and pepper.