Steam cauliflower until tender but still crisp. Drain and set aside.
Preheat the oven to 400°F (200°C).
Melt 2 tablespoons butter with chives and garlic in a 10 inch ovenproof skillet.
Whisk in flour and cook for 1 minute.
Slowly add heavy cream and ⅔ cup milk. Whisk until bubbly and slightly thickened.
Season with salt, black pepper, sage, and cayenne. Remove from heat.
Stir in cauliflower and coat with creamy sauce.
Top with shredded cheese.
Mix bread crumbs, Parmesan, and remaining 2 tablespoons melted butter.
Sprinkle mixture over cauliflower.
Bake for 30 minutes until hot, bubbly, and golden.
Garnish with parsley if desired.