01 - Preheat oven to 400°F (200°C). Pierce the scrubbed potatoes thoroughly with a fork. Place them on a baking sheet and roast until tender, approximately 50-60 minutes. Allow them to cool slightly, then peel and roughly chop.
02 - While potatoes are roasting, cook the bacon in a large soup pot over medium heat until crisp. Transfer cooked bacon to a plate lined with paper towels to drain. Once cooled, crumble the bacon. Reserve 1 tablespoon of bacon fat in the pot, discarding the excess.
03 - Add the butter to the reserved bacon fat in the soup pot. Sauté the finely chopped onion over medium heat until softened, about 5 minutes. Stir in the minced garlic and cook for an additional minute until fragrant.
04 - Whisk in the cornstarch (or gluten-free flour) and cook for 1 minute. Gradually incorporate the milk and heavy cream, scraping the bottom of the pot to loosen any browned bits.
05 - Add the chopped baked potatoes, salt, black pepper, and optional smoked paprika to the pot. Bring the mixture to a simmer and cook for 10-15 minutes, stirring occasionally, allowing the flavors to meld and the soup to thicken.
06 - Using a potato masher or an immersion blender, partially mash some of the potatoes directly in the soup to achieve a thicker consistency while retaining some potato chunks for texture. Stir in the shredded cheddar cheese until fully melted, followed by the sour cream.
07 - Adjust seasoning as necessary. Ladle the hot soup into individual bowls. Garnish generously with crumbled bacon, additional shredded cheddar cheese, a dollop of sour cream, and a sprinkle of freshly sliced scallions or chives.