Heat oven to 400℉
Wash potatoes, prick a few times with a fork, then bake at 400℉ for 1 hour or until done and tender. Let cool. Cut potatoes in half lengthwise and scoop out the good bits. Keep the skins.
Melt butter in heavy saucepan over low heat.
Add flour, stirring constantly.
Gradually add 4 cups of the milk.
Cook over medium heat, stirring constantly, until mixture thickens and bubbles.
Add potato pulp, salt, pepper, 2 tablespoons of the green onions, ½ cup of the bacon, and 1 cup of the shredded cheese.
Cook until heated through.
Stir in sour cream. Taste and adjust seasonings. Add more milk and heat if the consistency is too thick.
Serve with remaining onion, bacon, and cheese sprinkled on top.