Celeriac and Leek Gratin with Hazelnut-Panko Crust
Velvety layers of thinly sliced celeriac nestle against sweet, caramelized leeks and a silky cream-cheese sauce, finished under a golden, crunchy hazelnut-panko crust. The contrast of the soft, almost potato-like celeriac and the bright, toasty topping gives each bite satisfying texture and layered flavors.
Choose a firm celeriac and trim leeks carefully to remove grit; thin slices let the gratin cook evenly and the cream warm through. Swap Gruyère for fontina or a sharp cheddar for a more pronounced tang. For a lighter version use half-and-half instead of heavy cream and reduce the cheese by 25%.
Serve this gratin alongside roasted meats, a winter roast chicken, or as the centerpiece for a vegetarian supper with a crisp green salad. It makes a festive side for New Year gatherings and is make-ahead friendly — reheat gently in the oven and refresh the topping under the broiler for 2–3 minutes before serving.
How to Make It
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1
Preheat the oven to 190°C (375°F). Butter a 23x33 cm (9x13 inch) baking dish.
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2
Peel the celeriac and slice it into 2–3 mm rounds using a sharp knife or mandoline. Place slices in a bowl of cold water to prevent browning, then drain and pat dry.
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3
Trim and halve the leeks lengthwise; rinse thoroughly to remove grit, then slice into 3–4 mm half-moons.
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4
Heat 1 tbsp butter and the olive oil in a large skillet over medium heat. Add the leeks and a pinch of salt and cook, stirring occasionally, until soft and beginning to brown, 8–10 minutes. Add the garlic in the last minute and cook until fragrant. Remove from heat.
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5
Melt the remaining 2 tbsp butter in a saucepan over medium heat. Whisk in the flour and cook for 1 minute. Gradually whisk in the milk and cream until smooth. Simmer gently for 3–4 minutes until slightly thickened.
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6
Remove the sauce from the heat and stir in 150 g grated Gruyère, 30 g Parmesan, thyme, nutmeg, salt and pepper until the cheese melts and the sauce is smooth.
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7
Layer half of the celeriac slices in the prepared dish overlapping slightly. Spread the sautéed leeks over the celeriac, then pour half of the cheese sauce over. Add another layer of celeriac and pour the remaining sauce over the top, pressing gently so the sauce fills between slices.
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8
Mix the chopped toasted hazelnuts with the panko, the remaining 50 g Gruyère, the remaining 20 g Parmesan, lemon juice, and a pinch of salt and pepper. Sprinkle the mixture evenly over the gratin.
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9
Cover the dish loosely with foil and bake for 30 minutes. Remove the foil and bake uncovered until the top is golden and the celeriac is tender when pierced with a knife, 12–15 minutes more.
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10
If desired, broil on high for 1–2 minutes to crisp the topping further—watch closely to avoid burning. Let rest 10 minutes before serving to set the sauce.
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