How to Make It
In a large saucepan, melt the 2 tablespoons of butter. Add the celery and onion and cook over low heat until softened, about 6 minutes. Add the stock and milk and bring to a simmer over high heat. Add the cauliflower, sunchokes and thyme and bring to a boil. Simmer over low heat until the sunchokes are very tender, about 30 minutes; discard the thyme sprig.
Meanwhile, preheat the oven to 350°. In a small bowl, mix the 2 teaspoons of softened butter with the garlic and season with salt. Spread the garlic butter on the baguette slices and place on a baking sheet. Sprinkle with the cheese and bake for about 8 minutes, until crisp.
Working in batches, puree the soup in a blender until smooth. Return the soup to the saucepan; season with salt and pepper. Ladle into bowls and top with the sprouts. Serve with the cheese toasts.