Cut the beef bacon into 1-inch squares. Cook in a large pot over low heat until crispy, about 8-10 minutes. Remove and set aside, leaving 2 tablespoons of drippings in the pot.
Peel and cube the russet potatoes. Boil in a stockpot with 1 inch of water and salt for about 20 minutes until very tender. Drain and mash gently. Set aside.
Add diced onion to the pot with bacon drippings. Cook until softened, about 5 minutes. Add garlic and butter, cooking for an additional minute.
Whisk in flour and cook for 1 minute to remove the raw flour taste.
Pour in chicken broth, scraping any bacon bits from the bottom for flavor. Slowly add half and half, bring to a boil, then simmer.
Stir in the mashed potatoes, sour cream, and pepper. Remove from heat. For a smoother consistency, blend with an immersion blender or in batches in a regular blender.
Gradually add shredded cheese, stirring until combined. Ensure the soup isn't too hot, or the cheese won't melt smoothly. The soup will thicken as it cools.
Garnish with chives and bacon before serving.
Notes
For a vegetarian option, omit the bacon and use vegetable broth instead of chicken broth.