Preparation

• Preheat oven to 400˚F. Grease a 3 quart baking dish with butter.
• Slice sweet potato, parsnips, and beets into very thin rounds (using a mandoline is easiest) and transfer each vegetable to its own bowl.
• Pour 4 tablespoons cream over each sweet potato and parsnips, and 2 tablespoons cream over beets. Top each bowl of sliced vegetables with ½ ounce grated Parmesan and 1 teaspoon minced thyme. Season each bowl generously with salt and pepper and toss together until all vegetable slices are well coated.
• Pour remaining ¼ cup cream into the bottom of a 3 quart (oval) baking dish and sprinkle with ½ ounce of Parmesan and minced garlic.
• Grab a stack of sweet potatoes and line them standing up on a bias, at the top of the baking dish. Follow the sweet potato with a row of parsnips, followed by a row of beets. Repeat with the remaining sweet potatoes, parsnips, and beets, creating 6 rows of root vegetables.
• Season top of gratin with salt, pepper and sprinkle of remaining Parmesan.
• Cover with foil and bake for 30 minutes or until vegetables are soft.
• Uncover gratin and top with shredded gruyere.