Bake the Potatoes: Preheat your oven to 350°F (175°C). Scrub the potatoes clean, pat them dry, and pierce each several times with a fork. Rub each potato with olive oil and sprinkle with kosher salt. Place them directly on the oven rack and bake for about 1 hour, or until tender. Once done, let them cool slightly, then cut into bite-sized pieces.

Cook the Bacon: In a large pot or Dutch oven over medium heat, cook the chopped bacon until crisp. Remove the bacon bits and set them aside, leaving the rendered fat in the pot.

Sauté Aromatics: Add the unsalted butter to the pot with the bacon fat. Once melted, add the diced onion and cook until translucent, about 5 minutes. Stir in the minced garlic and cook for an additional minute.

Make the Roux: Sprinkle the all-purpose flour over the sautéed onions and garlic, stirring constantly for about 2 minutes to cook out the raw flour taste.

Add Liquids: Gradually whisk in the chicken broth until smooth. Add the heavy cream, stirring continuously. Bring the mixture to a gentle simmer.

Season the Soup: Stir in the celery salt, ground black pepper, dried basil, and granulated sugar. Let the soup simmer for about 5 minutes to allow the flavors to meld.

Incorporate Potatoes: Add the baked potato pieces to the pot, stirring gently to combine. Allow the soup to simmer for an additional 10 minutes, stirring occasionally.

Finish with Dairy: Stir in the shredded cheddar cheese until melted and smooth. Remove the pot from heat and blend in the sour cream until fully incorporated.

Serve: Ladle the soup into bowls and garnish with the reserved crispy bacon bits and chopped fresh chives.