Cook the bacon in a single layer in a Dutch oven over medium heat, flipping halfway, until browned and crisp, about 8 to 10 minutes. Transfer to a paper towel-lined plate.

Add the chopped onion to the bacon fat. Cook until softened, about 5 minutes.

Increase heat to high, add chicken broth, and scrape up any browned bits from the bottom. Stir in whole milk, kosher salt, and black pepper. Bring to a boil.

Add the peeled and chopped russet potatoes and bring to a simmer. Simmer until the potatoes are tender, about 8 to 10 minutes.

Crumble the bacon into small pieces.

Turn off the heat. Puree the soup in batches in a blender until smooth, or blend directly in the pot with an immersion blender. For a chunkier soup, blend half or smash the potatoes to desired consistency.

Return to low heat and stir in shredded cheddar cheese until melted. Off the heat, stir in sour cream, then taste and adjust seasoning.

Serve garnished with crumbled bacon, chopped chives, and more shredded cheddar cheese as desired.