Cook the chopped bacon in a large Dutch oven or soup pot over medium heat until crispy, about 8-10 minutes. Remove bacon with a slotted spoon and set aside on paper towels, leaving the bacon grease in the pot.

Add diced celery and onion to the bacon fat and cook until softened, about 5 minutes. Add minced garlic and cook for another 30 seconds until fragrant.

Add the cubed potatoes to the pot along with chicken broth. Bring to a boil, then reduce heat and simmer until potatoes are fork-tender, about 15-20 minutes.

In a separate saucepan, melt butter over medium heat. Whisk in flour to create a roux and cook for 1-2 minutes until lightly golden.

Slowly whisk in milk and heavy cream until smooth, then cook until the mixture thickens slightly, about 5 minutes.

Pour the cream mixture into the potato pot and add dried thyme, salt, and pepper. Stir well to combine.

Using an immersion blender, partially blend the soup to your desired consistency, leaving some potato chunks for texture. If you don't have an immersion blender, transfer about half the soup to a regular blender, blend until smooth, then return to the pot.

Stir in shredded cheddar cheese until melted. Add sour cream and stir until incorporated.

Reserve some bacon for garnish, and stir the rest into the soup.

Serve hot, garnished with reserved bacon bits, sliced green onions, and additional shredded cheese if desired.