In a large soup pot, heat olive oil over medium heat. Add onion and garlic. Cook until fragrant and translucent, about 3–4 minutes.
Stir in chopped cauliflower and vegetable stock. Bring to a boil, then reduce heat to a gentle simmer. Cook uncovered for 15–20 minutes until cauliflower is soft.
Remove from heat and puree using an immersion blender until smooth and creamy. (Alternatively, blend in batches using a countertop blender.)
Stir in milk and season with salt and white pepper. Warm gently without boiling. Add truffle oil and stir to combine.
In a small skillet, melt butter over medium heat until golden and nutty. Add breadcrumbs and toast, stirring constantly, until evenly browned.
Ladle soup into bowls. Sprinkle with brown butter breadcrumbs, drizzle extra truffle oil, and garnish with herbs or edible flowers.
