Unsalted butter, for preparing baking dish
1/2 large celery root (about 1 pound)
6 tablespoons olive oil, divided
1 pound red bliss potatoes
2 medium Bartlett pears,
Sea salt and freshly ground pepper, to taste
3/4 cup heavy whipping cream
1 garlic clove, smashed
1 cup (about 3 ounces) grated Gruyere cheese
2/3 cup (about 2 ounces) grated Parmesan cheese
1 teaspoon chopped fresh thyme
3/4 cup toasted panko breadcrumbs (optional)
Preheat oven to 375 F. Lightly butter a shallow 2-quart baking dish.
Line a baking sheet with paper towels.
Peel the celery root, then quarter it and slice 1/4 inch thick. In a large skillet, heat 2 tablespoons of the olive oil over medium heat. Working in batches, add celery root to skillet in a single layer and cook, turning, until browned, about 6 to 8 minutes per batch. Remove with a slotted spoon and drain on paper towels.
Meanwhile, peel the potatoes and slice them 1/4 inch thick. Add another 2 tablespoons olive oil (if needed) to skillet. Working in batches, add potatoes in a single layer and cook, turning, until browned and almost tender, about 10 minutes per batch. Remove with a slotted spoon and drain on paper towels with celery root.
Meanwhile, peel the pears, core them and slice 1/4 inch thick. Add remaining olive oil (if needed) to skillet. Add pear slices in a single layer and cook, turning, until browned, about 6 to 8 minutes; transfer to paper towels. Lightly season celery root, potatoes and pear with the salt and pepper.
In a saucepan, heat the cream and garlic over medium-high heat until just simmering; remove from heat.
Combine the Gruyere, Parmesan, thyme and 1 teaspoon each salt and pepper in a bowl.
Spread celery root in prepared baking dish. Sprinkle one-third of cheese mixture on top. Remove garlic from cream, then pour one-quarter of cream over cheese. Layer potatoes on top, then sprinkle with another one-third of cheese mixture; pour another one-quarter of cream on top. Top with pear slices and sprinkle with remaining cheese mixture. Pour remaining cream over everything.
Cover dish with aluminum foil and bake 30 minutes, then uncover, sprinkle top with toasted panko breadcrumbs, if desired and bake until gratin is bubbly and browned, 5 to 10 more minutes. Let cool 15 minutes before serving.
Makes 8 servings.
— Recipe adapted by the Detroit Free Press from Food Network Magazine's November 2012 issue.