Preheat oven to 400°F. Scrub and dry the potatoes, prick each with a fork, and bake directly on the oven rack for 50–60 minutes until tender. Let cool slightly, then peel and roughly mash.

While potatoes are baking, cook bacon in a large pot over medium heat until crispy. Remove and drain on paper towels. Crumble when cooled.

In the same pot with bacon drippings, add butter and diced onion. Cook for 5 minutes until translucent. Stir in flour to form a roux and cook for 1–2 minutes.

Gradually whisk in milk, breaking up any lumps. Stir in mashed potatoes and simmer for 10 minutes.

Reduce heat to low. Add sour cream and cheddar cheese. Stir until melted and smooth. Season with salt and black pepper.

Serve hot, garnished with crumbled bacon, extra cheddar, chopped green onions, and optional sour cream dollop.