Toss the cauliflower florets in the oil along with the salt and pepper and arrange them in a single layer on a large baking sheet.
Roast the cauliflower in a preheated 400F oven until lightly golden brown, about 20-30 minutes.
Heat the oil in a large sauce pan over medium heat.
Add the onion and saute until tender, about 5-7 minutes.
Add the garlic and thyme and saute until fragrant, about a minute.
Add the broth and cauliflower, bring to a boil, reduce the heat and simmer, covered, for 20 minutes.
Puree the soup until it reaches your desired consistency with a stick blender.
Mix in the cheese, let it melt and season with salt and pepper.
Mix in the milk and heat, stirring until soup is hot and cheese has melted.
Serve soup garnished with bacon if desired