Cauliflower Casserole (Casserole de Chou-Fleur)

Ingredients

• 1 large head of cauliflower, cut into florets
• 2 tablespoons olive oil or butter
• 2 cloves garlic, minced
• 1 small onion, finely chopped
• 3 tablespoons all-purpose flour
• 2 cups milk
• 1 cup grated Gruyère cheese (or cheddar if preferred)
• 1/2 cup grated Parmesan cheese
• 1/4 teaspoon nutmeg
• Salt
• pepper
• 1/2 cup breadcrumbs (for topping)
• 2 tablespoons melted butter (for topping)
• Fresh parsley, chopped (for garnish)