Ingredients

• 4 cups whipping cream, divided
• 2 tablespoons chopped fresh thyme
• 15 whole black peppercorns
• 5 large garlic cloves, crushed, divided
• 5 pounds long slender russet potatoes, peeled, cut into 1/8-inch-thick slices
• 3 fresh black truffles or three 1/3-ounce jars whole black truffles, sliced paper-thin

Instructions

1. Combine 2 cups cream, chopped thyme, black peppercorns, and 3 garlic cloves in heavy medium saucepan. Bring to simmer over medium heat. Cover, reduce heat to medium-low, and simmer 15 minutes. Add remaining 2 garlic cloves. Cover; simmer 5 minutes. Strain cream into bowl.
2. Preheat oven to 400°F. Butter 13x9x2-inch glass baking dish. Arrange 1/4 of potatoes in even layer in dish. Sprinkle with salt and pepper. Scatter 1/4 of truffle slices over. Spoon 1/4 of cream over. Repeat 3 more times, sprinkling any truffle liquid from jars over potato layers. Pour 2 cups cream over. Press potatoes firmly to compact. Cover dish with foil.
3. Bake gratin 1 hour. Uncover and bake until top is brown, potatoes are tender, and cream bubbles thickly, about 20 minutes longer. Let stand 10 minutes before serving.