Peel and cube 4 large russet potatoes into 1-inch pieces, then place them in a bowl of cold water to prevent browning and rinse away excess starch.

In a large dutch oven over medium heat, saute bacon pieces until crispy and golden. Remove bacon and set aside, leaving 1 tablespoon of bacon grease in the pot.

Add butter to the pot and let it melt completely. Add finely chopped onion and cook until translucent, about 3-4 minutes.

Stir in minced garlic and cook for 30 seconds until fragrant.

Whisk in flour and cook for 60 to 90 seconds, stirring constantly until light golden to create a roux.

Slowly pour in milk and chicken broth while whisking to prevent lumps. Bring mixture to a gentle simmer.

Drain potatoes and add them to the pot. Reduce heat and simmer for about 10 minutes until potatoes are tender enough to pierce easily with a fork.

Using a potato masher, lightly mash some potatoes in the pot, leaving some chunks for texture while creating creaminess.

Season with salt and pepper to taste. Stir in sour cream, shredded cheddar cheese, and most of the cooked bacon (reserve some for topping).

Bring soup back to a gentle simmer, then turn off heat. Serve immediately topped with reserved bacon, extra cheese, sour cream, and chopped green onions.