Cook the bacon in a large Dutch oven over medium heat until crispy. Remove bacon pieces, leaving the rendered fat in the pot.

Melt the butter in the pot with the bacon fat. Add chopped onion and sauté until tender (3-5 minutes). Stir in minced garlic and cook until fragrant (about 30 seconds).

Sprinkle flour over the mixture, stirring until smooth. Add potatoes, chicken broth, milk, heavy cream, salt, pepper, and ancho chili powder. Stir thoroughly.

Bring the soup to a boil, cooking until potatoes are fork-tender (10 minutes).

Puree half the soup in a blender or with an immersion blender and return to the pot. Stir in sour cream and reserved bacon pieces.

Simmer for 15 minutes to meld flavors.

Serve with optional toppings like shredded cheddar cheese, chives, or extra bacon.