Roasted Root Vegetable Gratin

Instructions

1. Prepare the baking dish
   Preheat the oven to 375°F (190°C). Butter a 9x13 inch baking dish or a large cast-iron skillet. Set aside.
2. Prepare the vegetables
   Wash, peel, and slice all root vegetables to approximately 1/8-inch thickness. Using a mandoline will ensure even slices and consistent cooking. Place sliced vegetables in a large bowl of cold water to prevent browning while you prepare the remaining ingredients.
3. Make the cream mixture
   In a saucepan, combine the heavy cream, minced garlic, 1 tablespoon of thyme, and all of the rosemary. Bring to a simmer over medium heat, then remove from heat. Add 1 teaspoon of salt and 1/2 teaspoon of pepper. Allow the mixture to steep for 10 minutes to infuse the flavors.
4. Layer the vegetables
   Drain the vegetables and pat them dry with paper towels. Begin layering the vegetables in the prepared dish, alternating between the different types for a colorful presentation. After each layer, sprinkle with a little salt, pepper, and some of the Gruyère cheese.
5. Add the cream and cheese
   Pour the infused cream mixture evenly over the layered vegetables. Sprinkle the remaining Gruyère and all of the Parmesan cheese on top. Dot the surface with the pieces of butter and sprinkle with the remaining thyme leaves.
6. Cover and bake
   Cover the dish with aluminum foil and bake for 45 minutes. The foil will trap steam and help cook the vegetables evenly.
7. Finish baking uncovered
   Remove the foil and continue baking for another 30 minutes, or until the top is golden brown and bubbling, and the vegetables are tender when pierced with a knife.
8. Rest and serve
   Allow the gratin to rest for 15 minutes before serving. This helps the layers set and makes it easier to serve neat portions. Garnish with additional fresh herbs if desired.