Parsnip Gratin with Caramelized Onions and Walnut-Panko
Silky tender parsnip slices are layered with deeply caramelized onions, a touch of garlic, and a cream-and-cheese sauce, then baked until bubbling and crowned with toasty walnut-panko for crunch and herbal brightness. The result mixes soft, creamy textures with crisp topping and a faint nutty edge from Gruyère.
Swap ingredients to match pantry or dietary needs: use half-and-half or full-fat milk with a tablespoon of butter in place of heavy cream for a lighter sauce, or swap Gruyère for sharp white cheddar or fontina. For a gluten-free version, replace panko with gluten-free breadcrumbs or extra finely chopped toasted walnuts.
Serve warm as a Thanksgiving or holiday side alongside roast turkey, pork, or a winter roast, or bring it to potlucks and family dinners where make-ahead convenience helps—assemble up to a day ahead and refrigerate, then finish baking before serving. Leftovers reheat well in a low oven to restore crispness on the topping.
How to Make It
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1
Preheat the oven to 190°C (375°F). Butter a 9x13-inch (or similarly sized) baking dish.
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2
Peel the parsnips and slice them 3–4 mm thick on a mandoline or with a sharp knife for even cooking.
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3
Halve and thinly slice the onion; smash and mince the garlic.
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4
Heat 1 tablespoon olive oil and 1 tablespoon butter in a large skillet over medium heat. Add the sliced onion and a pinch of salt, cook, stirring occasionally, until deep golden and soft, about 20–25 minutes. Stir in the garlic in the last 2 minutes and remove from heat.
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5
Grate the Gruyère and Parmesan, then combine the cheeses in a bowl.
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6
Warm the heavy cream and milk in a small saucepan until just below simmering; stir in 1 teaspoon salt, 1/2 teaspoon pepper, and lemon zest, then remove from heat.
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7
Layer one-third of the parsnip slices in the prepared dish, overlap slightly. Scatter one-third of the caramelized onions over the parsnips and sprinkle one-third of the cheese. Repeat two more times to finish with a cheese layer on top.
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8
Pour the warm cream-milk mixture evenly over the layered parsnips; press gently so liquid settles between slices. Cover the dish tightly with foil.
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9
Bake covered for 35 minutes. Meanwhile, make the topping: pulse walnuts and panko in a food processor until coarse crumbs form. Melt 1 tablespoon butter in a small pan, stir in the walnut-panko mixture and cook over medium heat for 3–4 minutes until golden; add chopped thyme and a pinch of salt.
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10
Remove foil and continue baking the gratin another 20–25 minutes until edges are bubbling and parsnips are tender when pierced with a knife.
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11
Scatter the walnut-panko topping over the gratin and place under the broiler 1–2 minutes to crisp the topping, watching carefully to prevent burning.
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12
Let the dish rest 10 minutes before serving to set. Garnish with extra thyme leaves if desired.
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