In a 12-inch skillet cook onion and garlic in butter over medium heat for 3 minutes or until softened. Stir in Brussels sprouts and thyme. Cook for 4 minutes or until onions begin to brown. Add broth. Bring to boiling. Cook, stirring occasionally, for 3 to 4 minutes or until broth is nearly evaporated. Add whipping cream and nutmeg. Cook for 4 minutes or until mixture begins to thicken. Transfer to prepared baking dish. Stir in half of the cheese, all of the salt, and pepper. Sprinkle with remaining cheese.