1. In a large pot over medium-high heat, cook bacon, stirring occasionally, until crisp and browned, 6 to 8 minutes. Transfer to paper towels to drain. When cool enough to handle, crumble.
2. Discard all but 2 Tbsp. fat and return pot to medium heat. Add onion, garlic and thyme and sauté until onion is soft, about 7 minutes. Add potatoes and broth; bring to a boil. Reduce heat to low; simmer until potatoes are tender, 12 to 15 minutes. Working in batches, process in blender with sour cream until smooth. Season with salt and pepper.
3. Ladle soup into bowls and top with chives and bacon.