Preheat oven to 425°F (220°C). Toss cauliflower florets with olive oil, salt, and pepper on a large baking sheet. Roast for 20-22 minutes until tender with caramelized golden-brown edges.

Meanwhile, in a large Dutch oven over medium heat, fry chopped bacon until crispy (6-7 minutes). Transfer bacon with a slotted spoon to a paper towel-lined plate, reserving 1 tablespoon of bacon drippings in the pot.

Add diced onion to the hot pot with bacon drippings, cooking for 4 minutes until translucent. Stir in minced garlic, smoked paprika, and mustard powder for 1 minute until fragrant.

Add roasted cauliflower florets and broth. Bring to a gentle boil, then reduce heat to low and simmer for 5 minutes.

Using an immersion blender, purée soup directly in the pot until completely smooth and velvety (or blend in batches in a countertop blender).

Turn off heat. Stir in heavy cream and shredded sharp cheddar cheese one handful at a time until completely melted and silky. Season with salt and pepper to taste.

Ladle hot soup into bowls and garnish generously with crispy bacon crumbles, extra cheddar, and fresh sliced chives.