For the baked potatoes, preheat the oven to 375 degrees F. Pierce the potatoes all over with the tines of a fork. Place the potatoes on a foil-lined baking sheet and bake for 45-60 minutes, until tender. Potatoes can also be "baked" in the Instant Pot: add 1 cup water and trivet/basket, add potatoes, secure lid, cook on high pressure for 12 minutes, naturally release the pressure.
Remove the potatoes from the oven/Instant Pot and let them sit for about 20 minutes, until they are cool enough to handle (the potatoes can be baked several days in advance and refrigerated).
Cut the potatoes in half and scoop out the insides of the potatoes. If the potatoes have been chilled, dice the flesh of the potatoes into 1/2-inch pieces.
For the soup, in a 4-quart or larger pot, melt the butter over medium heat. When melted, add 1/4 cup of the flour and whisk to combine. Cook the mixture, whisking constantly, until lightly browned, 2-3 minutes.
In a liquid measuring cup (or blender), whisk together the milk and remaining 1/4 cup flour. Gradually whisk the mixture into the pot in several additions. Whisk to combine each addition of milk fully before adding more. Cook until the soup is bubbling and slightly thickened, about 5-10 minutes, stirring often.
Stir in the potato chunks and salt and pepper. Use a potato masher to break up the chunks of potatoes into smaller pieces.
Whisk in the cheddar cheese and stir over medium-low heat until completely melted. Stir in the green onions and sour cream.
Serve with additional toppings. The soup will thicken more as it cools.
Potatoes: you'll need about 6 cups of cooked, diced potatoes for the recipe. That's right around 4-5 medium uncooked russet potatoes (about 33-36 ounces).Chicken: this soup is really delicious with cooked, diced chicken stirred in after the cheese has melted.Nutrition Facts: the nutrition facts for this recipe were calculated based on the soup (but do not include the topping as those are added based on personal preference).