Heat a large stockpot over medium heat. Place the bacon in the pot and cook, turning occasionally, until crispy.
Transfer the bacon to a paper towel-lined plate.
Add onions, garlic, salt, and pepper to the pot.
Cook, stirring often, until the onions are tender and translucent, about 10 to 12 minutes.
Stir in potatoes, cauliflower, and broth. Bring to a boil over high heat.
Reduce to a strong simmer and cook, stirring occasionally, until the potatoes are very soft, about 15 to 20 minutes.
Puree the soup, using a blender in batches or an immersion blender. Season to taste with salt and pepper.
Transfer the soup to bowls.
Crumble the bacon over the soup and top with sour cream, chives, and cheese.