Heat oven to 450 degrees. Pour olive oil into large bowl. Add cauliflower, shallot and garlic and stir so that oil coats the vegetables. Sprinkle on turmeric, cumin, salt and pepper. Toss to coat. Place vegetables on a parchment or foil lined baking sheet. Roast for 25 to 30 minutes, turning cauliflower occasionally until cooked.
While cauliflower is roasting, bring stock to a simmer in a large pot. Add roasted cauliflower, shallot and garlic. Cook for 10 minutes on a low boil. Using a stick blender or a stand blender (working in batches) carefully blend until smooth. Add in half & half and stir. Taste and adjust seasoning.
Ladle soup into bowls, drizzle with olive oil and sprinkle on crispy pancetta. Serve immediately.