Creamy Root Vegetable Gratin

From the garden

• 3 lb root vegetables (potatoes, carrots, turnips, salsify, or any root that slices thin), scrubbed and sliced 1/8 inch thick
• 3 cloves garlic, 1 halved, 2 minced
• 4 sprigs fresh thyme, leaves stripped

From the pantry

• 1½ cups heavy cream
• 1 cup whole milk
• 2 tbsp butter, softened · for the dish
• 1 cup grated parmesan · Gruyère is the traditional choice if you have it
• ¼ tsp ground nutmeg
• salt · to taste
• black pepper

1. Heat the oven to 350°F. Rub a 2-quart baking dish all over with the cut face of the halved garlic clove, then butter it well: the garlic perfumes the whole gratin and the butter keeps the edges from catching.
2. Slice the roots about 1/8 inch thick and as evenly as you can. A mandoline or the slicing blade of a food processor earns its keep here, because even slices are what let a gratin cook through in one piece.
3. Warm the cream, milk, minced garlic, thyme leaves, nutmeg, a teaspoon of salt, and plenty of pepper in a wide pot until steaming. Slide in the sliced roots and simmer gently 5 minutes, stirring once, until the liquid thickens a little from their starch.
4. Layer the slices into the dish in overlapping rows, scattering two thirds of the cheese between the layers. Pour the seasoned cream over, press the top flat so the liquid comes almost level with the slices, and finish with the rest of the cheese.
5. Bake 60–70 minutes, until the top is deeply browned and a thin knife slides through the center with no resistance; tent with foil if it colors before it is tender. Rest 15 minutes before cutting, or it will run across the plate.