Cook the Bacon:

In a large Dutch oven or soup pot over medium heat, cook the chopped bacon until crisp and browned.

Remove the bacon with a slotted spoon and drain on paper towels, leaving the rendered fat in the pot.

Sauté the Aromatics:

Add the butter to the pot with the bacon fat and melt over medium heat.

Add the chopped onion and sauté until translucent, about 5 minutes.

Stir in the minced garlic and cook for an additional minute until fragrant.

Create the Roux:

Sprinkle the flour over the onion and garlic mixture, stirring continuously to form a roux.

Cook for about 2 minutes to eliminate the raw flour taste.

Add Potatoes and Liquids:

Gradually whisk in the chicken broth until smooth.

Add the diced potatoes, milk, heavy cream, salt, pepper, and ancho chili powder (if using).

Bring the mixture to a boil, then reduce the heat to a simmer.

Cover and cook until the potatoes are tender, about 15-20 minutes.

Blend the Soup:

Use an immersion blender to puree about half of the soup, leaving some chunks for texture.

Alternatively, transfer half of the soup to a blender, puree until smooth, and return it to the pot.

Finish the Soup:

Stir in the sour cream until fully incorporated.

Taste and adjust seasoning with additional salt and pepper if needed.

Serve:

Ladle the soup into bowls and top with shredded cheddar cheese, chopped chives, and reserved bacon pieces, if desired.