- 2 cups heavy cream
- 2/3 cups whole milk
- 1 garlic clove, crushed and peeled
- 1 pound Yukon Gold potatoes, peeled and sliced into 1/8-inch-thick rounds
- 1 pound rutabaga, peeled and sliced into 1/8-inch-thick rounds
- 1 teaspoon kosher salt
- 1/2 teaspoon freshly ground black pepper
- 1/2 freshly grated nutmeg
- 4 smoked mackerel fillets, broken into pieces
- Arrange oven rack in middle position and preheat oven to 350��F. Butter 9-inch-diameter pie plate.
- In small heavy saucepan, combine cream, milk, and garlic. Bring to boil over moderately high heat, then remove from heat and set aside.
- Layer 1/4 of potatoes in baking dish in concentric circles, overlapping slightly. Sprinkle with 1/4 teaspoon salt, 1/8 teaspoon pepper, and 1/8 teaspoon nutmeg, then pour 1/2 cup cream mixture over. Repeat process using rutabaga instead of potatoes to make second layer.
- Scatter mackerel pieces over root vegetables and top with 1/2 cup cream mixture. Make another layer of rutabaga, then final layer of potatoes, topping final layer with remaining 2/3 cup cream mixture.
- Bake until potatoes are tender when pierced with knife and top is golden, about 45 to 55 minutes. Let gratin stand 5 minutes before serving.