Preheat your oven to 400˚F. Grease a 3-quart baking dish with butter. prep

Slice the sweet potatoes, parsnips, and beets into thin rounds (using a mandoline for even slices). Transfer each vegetable to a separate bowl. prep

Pour 4 tablespoons of cream over the sweet potatoes and parsnips, and 2 tablespoons over the beets. Top with ½ ounce of grated Parmesan and 1 teaspoon of thyme in each bowl. Season generously with salt and pepper, then toss to coat the vegetables evenly. mix

Pour the remaining ¼ cup of cream into the bottom of the prepared baking dish. Sprinkle with ½ ounce of Parmesan and the minced garlic. assemble

Assemble gratin base

Begin layering the vegetables: start with sweet potatoes standing on their side, followed by parsnips and beets in rows. Repeat until the dish is filled, creating six rows of vegetables. assemble

Season the top layer with salt, pepper, and sprinkle with the remaining Parmesan. bake

Cover the dish with foil and bake for 30 minutes, or until vegetables are tender. bake

Remove the foil and top the gratin with shredded gruyere. Return the dish to the oven, uncovered, and bake for an additional 18–20 minutes until the cheese has melted and the top is golden. bake

Finish by sprinkling fresh thyme on top. Serve hot and enjoy. finish