01 -
Preheat oven to 400˚F. Grease a 3 quart baking dish with butter.
02 -
Slice sweet potato, parsnips and beets into very thin rounds (using a mandoline is easiest) and transfer each vegetable to its own bowl.
03 -
Pour 4 tablespoons cream over sweet potatoes and parsnips, and 2 tablespoons cream over beets. Top each bowl with ½ ounce grated Parmesan and 1 teaspoon minced thyme. Season with salt and pepper and toss until well coated.
04 -
Pour remaining 1/4 cup cream into the bottom of the baking dish and sprinkle with ½ ounce of Parmesan and minced garlic.
05 -
Grab a stack of sweet potatoes and line them standing up on a bias, at the top of the baking dish. Follow with a row of parsnips, followed by a row of beets. Repeat with the remaining vegetables, creating 6 rows.
06 -
Season top with salt, pepper and sprinkle of remaining Parmesan. Cover with foil and bake for 30 minutes or until vegetables are soft.
07 -
Uncover gratin and top with shredded gruyere. Continue to bake uncovered for an additional 18 to 20 minutes or until vegetables are fork tender and cheese has melted and lightly browned.
08 -
Finish with a sprinkle of fresh thyme leaves and serve.