1 1/2 cups (360 ml) heavy cream
1 cup (240 ml) chicken broth
2 cloves garlic, minced
1 teaspoon (1 g) dried thyme
2 teaspoons (14 g) salt
1 teaspoon (2 g) pepper
3 medium sweet potatoes, peeled and thinly sliced
6 small Yukon gold potatoes, peeled and thinly sliced
4 turnips, peeled and thinly sliced
3 large celery roots (celeriac), thinly sliced
2 cups (200 g) Pecorino Romano
2 cups (250 g) bread crumbs
2 tablespoons (28 g) butter, melted
Heat oven to 350 degrees Fahrenheit (175 degrees Celsius). Butter a 13-by-9-inch baking dish.
Mix together thyme, salt, pepper, cream and chicken broth in a large bowl.
Layer root vegetables in dish, in the order listed, creating a single layer of each vegetable. Sprinkle with 3/4 cup cheese and pour 3/4 cup cream mixture over the top.
Repeat, making another single layer of each vegetable, adding another 3/4 cup cheese and 3/4 cup cream mixture.
Layer the remaining vegetables on top. Pour in the rest of the cream mixture.
Mix remaining 1/2 cup cheese with melted butter and bread crumbs and sprinkle on top. Bake for 1 hour, 15 minutes, until vegetables are tender. Cool for at least 10 minutes before serving.