Sauté the onion and garlic: In a large Dutch oven or soup pot, melt the butter over medium heat. Add the diced onion and cook until soft and translucent, about 5–6 minutes. Add the garlic and cook for 30 seconds until fragrant.

Make the roux: Sprinkle the flour over the onion mixture. Stir continuously and cook for 1–2 minutes to remove the raw flour taste. Slowly whisk in 4 cups of chicken broth, followed by the milk, stirring until smooth. Bring to a low boil, stirring frequently and scraping the bottom of the pot to prevent the milk from scorching.

Add the potatoes and season: Stir in the diced potatoes, Better Than Bouillon, and salt. Reduce the heat and simmer uncovered until the potatoes are fork-tender, 15–20 minutes.

Blend until creamy: Remove 2–3 cups of the cooked potatoes, depending on how chunky you’d like the soup. Blend the remaining soup until smooth using an immersion blender or blender. Slowly add the remaining 2 cups of chicken broth, 1 cup at a time, as needed to thin the soup to desired consistency.

Finish the soup: Stir the reserved potato chunks back into the soup. Taste and adjust seasoning as needed.

Serve: Ladle into bowls and top with cheddar cheese, green onions, bacon, and sour cream if desired.