1 pound Yukon Gold potatoes, peeled and sliced thin
8 ounces parsnips, peeled and sliced thin
8 ounces carrots, peeled and sliced thin
8 ounces sweet potatoes, peeled and sliced thin
2 cups heavy cream
3 cloves garlic, minced
1 tablespoon fresh thyme leaves
1 tablespoon fresh rosemary, finely chopped
1.5 cups shredded Gruyere cheese
0.5 cup grated Parmesan cheese
1 teaspoon sea salt
0.5 teaspoon ground black pepper
1 tablespoon unsalted butter for greasing the dish
Instructions
Preheat your oven to 375 degrees F. Take your butter and generously grease a 9 by 13 inch baking dish or a deep oval gratin dish. This prevents sticking and adds a little extra golden crust to the bottom layer of vegetables.
Using a sharp knife or a mandoline slicer, cut the potatoes, parsnips, carrots, and sweet potatoes into very thin rounds, about 1/8 inch thick. Keeping the slices uniform is the secret to ensuring that every vegetable cooks through at the same rate.
In a small saucepan over medium heat, combine the heavy cream, minced garlic, fresh thyme, and rosemary. Heat the mixture until it just begins to simmer, then remove it from the heat. Stir in the salt and pepper. This infusion process ensures the garlic and herb flavors are distributed evenly throughout the entire dish.
Arrange a layer of the mixed vegetable slices in the bottom of your prepared dish. Sprinkle a handful of the Gruyere and Parmesan cheese over the top. Repeat the layers until all the vegetables are used. Pour the warm, herb infused cream over the top of the vegetables, pressing down gently with a spatula to make sure the liquid settles into all the crevices.
Cover the dish tightly with aluminum foil and bake for 40 minutes. This steams the vegetables until they are tender. After 40 minutes, remove the foil and sprinkle any remaining cheese on top. Bake for another 15 to 20 minutes until the top is bubbly and golden brown. Let the gratin rest for 10 minutes before serving to allow the sauce to thicken.
