Preheat the oven to 400 degrees F.
Wash the potatoes and prick them several times with a fork. Wrap them individually in foil and bake until they are soft when squeezed, about 1 hour (see Cook's Note). Let the potatoes cool slightly.
While the potatoes bake, cook the bacon in a small skillet, in a microwave or on an indoor grill until crisp. Drain the bacon on paper towels and, when cool enough to handle, crumble into small pieces. Set aside.
In a large heavy saucepan, melt the butter over low heat. Add the flour, stirring constantly for 1 minute until smooth. Gradually whisk in the milk and cook over medium heat, stirring constantly, until the mixture is thick and bubbling, 5 to 10 minutes. Cut the potatoes in half lengthwise and scoop the flesh into the thickened milk mixture. Add the Cheddar, salt, pepper, green onions and reserved bacon. Cook over low heat just until heated through, then stir in the sour cream. Garnish with shredded Cheddar, crumbled bacon and chopped green onions and serve with more sour cream on the side.
Wrapping the potatoes in foil before baking makes them cook faster. To shorten the preparation even more, peel the potatoes, cut them up into 1-inch cubes and cook them in a pressure cooker for 5 minutes. Leftover baked potatoes may also be used for this recipe. Peel and mash them coarsely before adding to the milk mixture.
Adapted from "Georgia Cooking in an Oklahoma Kitchen: Recipes from My Family to Yours" by Trisha Yearwood © Clarkson Potter 2008. Provided courtesy of Trisha Yearwood. All rights reserved.