This gratin is inspired by a traditional gratin dauphinois, but incorporates layers of zucchini to bring more color and fiber to a hearty, comforting dish. I also leave the skin on the potatoes for additional crispiness and texture. —Jill Haapaniemi
Preheat oven to 400°F. In a saucepan over medium-low heat, add milk, cream, garlic, and thyme. Warm until bubbles begin to form around edges of pan; remove from heat. Stir in nutmeg.
In a lightly greased baking dish, layer half of the potato slices in rows, just overlapping, until bottom of dish is covered. Over potatoes, layer half of zucchini slices in rows, just overlapping, until potatoes are covered. Season with 1/4 teaspoon salt and 1/8 teaspoon pepper. Pour half of milk mixture over vegetables. Repeat with remaining potatoes, zucchini, salt, pepper, and milk. Sprinkle evenly with gruyère, cover with foil and bake 1 hour.
Remove foil. Bake until cheese begins to brown and edges become crisp, 10 more minutes. Garnish with fresh chives, if desired.