1. In a large pot, heat butter or olive oil over medium. Add slices from leeks; season with salt. Cook 5-7 minutes, stirring frequently, until leeks are wilted.
2. Add thyme and chili powder; stir 30 seconds. Pour in water, then potatoes, followed by bay leaves. Cover and simmer until potatoes are tender, 15 to 30 minutes.
3. Discard bay leaves; purée soup in a blender, seasoning with more salt if desired. Garnish with bacon crumbles, grated cheddar, and chives.