Preheat your oven to 400°F (200°C) for Parmesan tuiles. On a baking sheet lined with parchment paper, arrange small mounds of grated Parmesan cheese, spacing them apart. Lay prosciutto slices on another sheet to bake until crispy, about 10-15 minutes.

Lower the oven temperature to 375°F (190°C). Toss cauliflower florets in extra virgin olive oil and sprinkle with kosher salt. Spread them on a baking sheet and roast for 40 minutes.

In a large pot over medium heat, melt unsalted butter. Add diced onions and sauté for about 5-7 minutes until translucent. Add black pepper and dried thyme.

Combine roasted cauliflower, sautéed onions, vegetable stock, minced garlic, and ground coriander in the pot. Bring to a gentle boil over medium-high heat. Reduce heat and let it simmer uncovered for 20 minutes.

Blend the soup until smooth, using a high-powered blender or immersion blender. Return it to the pot and stir in heavy cream and grated asiago cheese, heating gently.

Taste and adjust seasoning. Ladle the soup into warm bowls and garnish with crispy prosciutto, Parmesan tuiles, and fresh thyme.