I'd never considered combining potatoes and parsnips before, except in a mash. Great idea, this! From famed Chef Charlie Palmer.
INGREDIENTS
•2 tablespoons olive oil
•4 medium garlic cloves, minced
•1 cup heavy cream
•1 tablespoon kosher salt
•Freshly ground black pepper
•Freshly ground nutmeg
•1 pound parsnips
•1 1/2 pounds russet potatoes
•4 tablespoons unsalted butter (1/2 stick), cut into small pieces, plus more for coating the baking dish
•1 cup shredded Emmentaler cheese (about 2 to 3 ounces)
•1 cup fresh breadcrumbs
INSTRUCTIONS
Heat the oven to 425°F and arrange a rack in the middle. Lightly coat a 2-1/2-quart baking dish with butter and set aside.
Heat the olive oil in a small saucepan over medium heat until shimmering, about 3 minutes. Add the garlic and cook, stirring occasionally, until softened but not browned, about 2 minutes. Add the cream and salt, season with pepper and a pinch of nutmeg, stir to combine, and cook until the cream is simmering but not boiling; remove from the heat and set aside.
Peel, trim, and slice the parsnips crosswise into 1/8-inch-thick rounds. Place in a large mixing bowl. Peel the potatoes, slice crosswise into 1/8-inch-thick rounds, and add to the bowl. Toss the potatoes and parsnips until evenly combined and set aside.
Evenly layer half of the potato-parsnip mixture in the prepared dish. Dot with half of the butter and sprinkle with half of the cheese. Evenly layer the remaining half of the potato-parsnip mixture in the dish and pour the warm cream mixture evenly over the top. Dot with the remaining butter and sprinkle with the remaining cheese.
Cover the dish with foil and bake until the potatoes and parsnips are tender when pierced with a fork, about 35 to 40 minutes.
Remove the foil and sprinkle the breadcrumbs evenly over the gratin, pressing them down lightly with the back of a spatula (this helps them absorb some of the moisture and keeps them from browning too fast). Return the gratin to the oven uncovered and bake until the top is golden brown, about 10 minutes more. Let rest at least 5 minutes before serving.