Cooking Instructions

• In a small saucepan, combine cream, milk, garlic, shallots, nutmeg, thyme, peppercorns, and salt. Bring to a boil, then remove from heat, cover, and let steep for 1 hour.
• Return milk mixture to boil, then strain into a large heatproof bowl, pressing gently on the solids.
• Using a mandoline, slice the peeled potatoes crosswise 1/16-inch (1.5mm) thick, directly into the hot milk mixture. Stir the potatoes to fully coat.
• Preheat oven to 350°F (177°C). In a small bowl, combine the Gruyère and Parmigiano-Reggiano cheeses.
• Grease a 2-quart baking dish with the butter. Lay the sliced potatoes in one even layer, then sprinkle with about ⅓ cup cheese mixture. Repeat layering potatoes and cheese until all the potatoes have been used and half the cheese mixture remains (you should have about 4 layers); leave the top layer without cheese. Pour any remaining milk mixture over the layered potatoes.
• Cover with aluminum foil and bake for 1 hour. Remove baking dish from oven and remove foil. Evenly sprinkle remaining cheese on top and continue to bake, uncovered, until the potatoes have become tender, the sauce has thickened, and the surface is lightly golden brown, 15 to 20 minutes.
• Allow the gratin to rest 30 minutes before serving.