"Create a recipe for Cheesy Potato Mushroom Gratin that serves 6 people. The recipe should include a rich and flavorful sauce made with heavy cream, half & half, garlic paste, fresh rosemary, thyme, nutmeg, and three types of cheese: cream cheese, Asiago, and Gruyere. The dish should also have sautéed mushrooms and blanched potatoes, topped with a crunchy Parmesan almond crumb and garnished with fresh chives. Prep time is 25 minutes and cooking time is 25-30 minutes. Use imperial units."