Turnip, Potato, and Smoked Mackerel Gratin

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.