2Place the cauliflower in a small roasting pan. Drizzle with oil and season with nutmeg, garlic powder, salt, and pepper; toss to coat.
3Roast the cauliflower in the preheated oven stirring every 10 minutes until golden brown and tender, 30 to 40 minutes. Remove from the oven and set aside.
4Melt the butter in a large saucepan over medium heat. Add the chopped onion and cook and stir until lightly golden brown, about 10 minutes.
5Sprinkle the flour over the onions and stir to coat. Slowly pour the chicken broth and milk into the pan. Mix with a wire whisk until all of the flour is dissolved. Bring to a boil while stirring continuously until it thickens, then reduce heat to low. Stir in the sherry and the roasted cauliflower. Serve as is, or blend half and recombine with the rest of the soup for a thicker consistency.