Position one oven rack 1/3 from top and one rack 1/3 from bottom. Line baking sheet with parchment paper. Preheat oven to 375 Toss cauliflower florets with oil and salt in a large mixing bowl. Spread cauliflower on baking sheet - wipe out bowl to use in next step. Bake cauliflower on lower rack 20 minutes then preheat broiler on Hi and transfer to upper rack and broil for 7 - 10 minutes until nicely browned and tender. KEEP BROILER ON Transfer cauliflower to bowl. Add cream, garlic, Gruyere cheese, /2 of the Parmigiano and all of the pepper and nutmeg. Toss to mix well and pour into a gratin dish. Sprinkle with remaining Parigiano and return to broil for 5 minutes until golden brown and bubbly. Serve hot.