In a large pot or Dutch oven over medium heat, cook the bacon pieces until crispy. Once done, remove the bacon and set it aside for later. Leave the bacon grease in the pot.
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In the same pot with the bacon grease, add the butter and sauté the chopped onions until they are translucent. Add the minced garlic and cook for an additional 1-2 minutes until fragrant.
Sprinkle the all-purpose flour over the onion and garlic mixture. Stir continuously to create a roux, cooking for 2-3 minutes to eliminate the raw flour taste.
Add the diced potatoes to the pot, stirring them into the roux mixture.
Slowly pour in the chicken broth and milk while stirring to avoid lumps. Add the heavy cream, salt, pepper, and ancho chili powder. Stir well to combine.
Bring the chowder to a simmer over medium heat. Reduce the heat to low and let it simmer until the potatoes are tender, about 15-20 minutes.
Stir in the sour cream and half of the cooked bacon. Taste and adjust seasoning if needed. Allow the chowder to heat through but avoid boiling after adding sour cream.
Serve hot, topped with shredded cheddar cheese, chives, additional sour cream, and bacon if desired.