Wash potatoes and prick several times with fork; bake at 400° for 1 hour or until done. Let cool. Cut potatoes in half lengthwise, then scoop out pulp; set aside. Discard skins. Melt butter in a heavy saucepan over low heat; add flour, stirring until smooth. Cook for one minute, stirring constantly. Gradually add milk; cook over medium heat, stirring constantly, until mixture is thickened and bubbly.

Add potato pulp, salt, pepper, 2 tbsp green onions, 1/2 cup bacon, and 1 cup cheese. Cook until thoroughly heated; stir in sour cream. Add extra milk, if too thick. Serve topped with remaining onion, bacon, and cheese.