01 - In a large pot or Dutch oven, cook the chopped bacon over medium heat until crisp. Using a slotted spoon, remove the bacon and drain on paper towels. Reserve 2 tablespoons of bacon fat in the pot.
02 - Add the unsalted butter to the reserved bacon fat. Sauté the finely chopped yellow onion and celery until softened, approximately 4–5 minutes. Stir in the minced garlic and cook for an additional 1 minute.
03 - Sprinkle the all-purpose flour over the softened vegetables. Stir constantly for 2 minutes to form a roux, ensuring no lumps.
04 - Gradually whisk in the low-sodium chicken broth, scraping the bottom of the pot to deglaze any browned bits. Add the whole milk and bring the mixture to a gentle simmer.
05 - Stir in the diced baked russet potatoes. Allow to simmer for 10 minutes, stirring occasionally. Lightly mash some of the potatoes with a potato masher to achieve a creamier texture, while leaving some chunks intact.
06 - Reduce the heat to low. Gently stir in the heavy cream, shredded sharp cheddar cheese, and sour cream until completely melted and the chowder is smooth.
07 - Season the chowder with salt and freshly ground black pepper to your preference. Stir in half of the cooked bacon. Heat through gently.
08 - Ladle the hearty chowder into individual bowls. Garnish generously with the remaining crispy bacon, thinly sliced green onions, fresh chives, additional shredded cheddar cheese, and a dollop of sour cream, as desired.