Heat a large stock pot to medium high heat. Add diced bacon, and cook until crisp. Remove from pan along with the bacon fat.
Use reserved bacon grease or butter as your fat, and add it to stock pot. Add carrots, celery, onion, bacon, and salt & pepper, and sauté until vegetables are softened, approximately 5-6 minutes. Add flour, and stir for 2-3 minutes, or until flour is absorbed fully.
Add chicken broth and milk, and stir well. Bring mixture to a boil, and add chopped potatoes. Reduce to a rolling simmer, and cook until potatoes are fork tender. Check seasonings, and add salt and pepper if needed.
Add sour cream and cheddar cheese, and stir until fully absorbed and melted into the soup. Remove from heat.
Optional step. If you want to make this EXTRA creamy, use an immersion blender to puree a portion of the soup. If you blend for about 20 seconds, that would be perfect. OR, use your regular blender - but make sure you let the soup cool a bit in the blender before you puree.
Serve soup with some extra cheese, bacon, green onions, and saltine crackers.