Preheat the oven to 400 degrees F. Scrub russet potatoes and pierce them with a fork. Place directly on the oven rack and bake until tender, about 50-60 minutes. Remove from oven, let cool, then peel and dice.

Meanwhile, in a skillet, cook bacon until crisp. Remove, drain on paper towels, crumble, and set aside. Reserve 2 tablespoons of bacon fat.

In a large pot, melt butter and reserved bacon fat over medium heat. Add chopped onion and garlic, sauté until opaque. Sprinkle flour over and stir to form a roux. Gradually pour in chicken broth, whole milk, and heavy cream, whisking continuously until smooth. Add diced potatoes, salt, and pepper. Bring to a boil, then reduce heat and simmer for 20 minutes.

Remove pot from heat. Stir in shredded cheddar cheese and sour cream until well combined. Serve hot, garnished with crumbled bacon and chopped chives.