The soup and garlic butter can be made a day ahead, so this is a
fantastic midweek winter meal. Leftover garlic butter will keep
refrigerated for two weeks. If you like your soup thinner, add
Heat butter and oil in a large saucepan over medium heat. Add onion, leek and garlic and stir occasionally until tender (7-10 minutes). Add cauliflower, stir to coat in butter, add stock and simmer until very tender (40-45 minutes). Add milk, bring to the simmer, then purée in a blender until very smooth. Stir in Gruyère, crème fraîche and mustard, season to taste and keep warm.
Meanwhile, for garlic toast, preheat grill to high. Process butter, parmesan, garlic and herbs in a food processor until smooth and season to taste. Place baguette slices on a baking tray, drizzle with oil, season to taste and grill, turning once, until golden (1-2 minutes). Spread with garlic butter and serve hot with cauliflower soup.