1 lb. rutabagas, peeled and thinly sliced
1 lb. sweet potatoes, peeled and thinly sliced
1 lb. Russet potatoes, peeled and thinly sliced
1 cup heavy cream
2 cloves garlic, chopped
1 tsp. chopped fresh thyme leaves
2 Tbs. kosher salt
1 Tbs. white pepper
2 cups grated Gruyere cheese
Preheat oven to 350°F. Butter a 10 x 13-inch rectangular casserole dish.
Bring a large saucepan of water to a boil over high heat. Add the rutabagas, sweet potatoes, and Russet potatoes and let them cook for three minutes. Drain and set aside.
Put the cream, garlic, thyme, salt, and pepper in a small saucepan over medium-high heat. Bring the mixture to a boil and reduce the heat to low. Simmer for three minutes. Remove the saucepan from the heat.
Spread a bit of the cream on the bottom of the casserole dish. Place a layer of rutabagas, sweet potatoes, and Russet potatoes on top. Follow with cream and cheese. Continue layering, ending with a layer of cheese.
Bake the gratin until it is bubbling on the sides and golden brown on top, 30 to 40 minutes.
