Truffled Potato Gratin
Ingredients:4 cups whipping cream, divided2 tablespoons chopped fresh thyme15 whole black peppercorns5 large garlic cloves, crushed, divided5 pounds long, slender russet potatoes, peeled, cut into 1/8-inch-thick slices3 fresh black truffles or three 1/3-ounce jars whole black truffles, sliced paper-thin