Preheat your oven to 400°F (200°C). Wash and dry the potatoes. Prick each potato with a fork to allow steam to escape during baking.

Place the potatoes directly on the oven rack and bake for about 1 hour, or until they are tender when pierced with a fork.

Once baked, remove the potatoes from the oven and let them cool slightly. Cut them in half lengthwise and scoop out the pulp into a bowl. Set aside.

In a large saucepan or stockpot, melt the butter over low heat. Add the flour to the melted butter, stirring constantly to create a smooth roux. Cook for about 1 minute, ensuring it doesn't brown.

Gradually whisk in the milk, increasing the heat to medium. Continue stirring until the mixture thickens and becomes bubbly.

Add the scooped potato pulp to the pot, breaking up any large pieces with a spoon. Season the soup with salt, black pepper, and white pepper.

Stir in most of the chopped green onions (reserving some for garnish), half of the crumbled bacon, and 1 cup of the shredded cheddar cheese. Cook the soup until it's thoroughly heated, but avoid bringing it to a boil.

Stir in the sour cream, mixing well to incorporate it into the soup. If the soup is too thick for your liking, add extra milk to achieve the desired consistency. Continue to heat the soup gently until it's hot, but do not let it boil.