Rustic Butter-Crusted Root Vegetable Gratin

Quick Recipe Version (TL;DR)

• Yield: 6 servings
• Prep Time: 30 minutes
• Cook Time: 1 hour 15 minutes
• Total Time: 1 hour 45 minutes

Quick Ingredients

• 1 1/2 lb (680 g) Yukon Gold potatoes, peeled and thinly sliced
• 10 oz (280 g) parsnips, peeled and thinly sliced
• 8 oz (225 g) carrots, peeled and thinly sliced
• 1 large yellow onion, thinly sliced
• 2 cloves garlic, minced
• 1 3/4 cups (415 ml) heavy cream + 1/2 cup (120 ml) whole milk
• 1 1/4 cups (125 g) grated Gruyère + 1/2 cup (50 g) sharp cheddar
• 5 tbsp (70 g) unsalted butter, divided
• 1/4 cup (15 g) dry breadcrumbs or panko
• 2 tsp fresh thyme, 1/4 tsp nutmeg, 1 tsp Dijon (optional)
• 1 1/2 tsp kosher salt, 3/4 tsp black pepper, plus extra to taste

Do This

• 1. Preheat oven to 375°F (190°C). Generously butter a 2-quart (about 8×11-inch) baking dish.
• 2. Gently heat cream, milk, garlic, thyme, nutmeg, Dijon, salt, and pepper until steaming; set aside to infuse.
• 3. Thinly slice potatoes, parsnips, and carrots (about 1/8 inch / 3 mm). Pat dry.
• 4. Sauté sliced onion in 1 tbsp butter and 1 tbsp oil with a pinch of salt until soft and lightly golden.
• 5. Layer vegetables in the dish, shingling potatoes, parsnips, and carrots with onion and cheese between layers; ladle in cream mixture as you go.
• 6. Mix melted butter, breadcrumbs, and remaining cheese; spread over top. Cover tightly with foil.
• 7. Bake covered 45 minutes, then uncovered 25–35 minutes until vegetables are tender and the top is deeply golden. Rest 10–15 minutes before serving.

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Why You’ll Love This Recipe

• Classic gratin comfort, but with extra flavor from sweet parsnips, carrots, and slow-cooked onions.
• A buttery, ultra-crisp top crust hides silky, tender layers underneath.
• Flexible side dish that works with roast chicken, steak, pork, or as a cozy vegetarian main with a salad.
• Great make-ahead option: assemble earlier, then bake when you are ready to eat.

Grocery List

• Produce: Yukon Gold potatoes, parsnips, carrots, yellow onion, garlic, fresh thyme (or dried).
• Dairy: Heavy cream, whole milk, unsalted butter, Gruyère cheese, sharp cheddar or Comté.
• Pantry: Olive oil, dry breadcrumbs or panko, Dijon mustard, ground nutmeg, kosher salt, black pepper.

Full Ingredients

For the Root Vegetable Gratin

• 1 1/2 lb (680 g) Yukon Gold or other all-purpose potatoes, peeled and sliced 1/8 inch (3 mm) thick
• 10 oz (280 g) parsnips, peeled and sliced 1/8 inch (3 mm) thick
• 8 oz (225 g) carrots, peeled and sliced 1/8 inch (3 mm) thick
• 1 large yellow onion (about 8 oz / 225 g), thinly sliced
• 2 cloves garlic, minced or very finely chopped
• 1 3/4 cups (415 ml) heavy cream
• 1/2 cup (120 ml) whole milk
• 2 tsp fresh thyme leaves, plus extra for garnish (or 1 tsp dried thyme)
• 1/4 tsp ground nutmeg
• 1 tsp Dijon mustard (optional but recommended for gentle tang)
• 1 1/2 tsp kosher salt, divided, plus more to taste
• 3/4 tsp freshly ground black pepper, divided, plus more to taste
• 5 tbsp (70 g) unsalted butter, divided:
  • 2 tbsp (28 g) for greasing the dish and sautéing onions
  • 3 tbsp (42 g) melted for the buttery crust
• 1 tbsp olive oil (for sautéing the onion)
• 1 1/4 cups (125 g) grated Gruyère cheese, divided
• 1/2 cup (50 g) grated aged sharp cheddar or Comté cheese
• 1/4 cup (15 g) dry breadcrumbs or panko
• Optional: pinch of flaky sea salt for serving

Step-by-Step Instructions

Step 1: Preheat the oven and prepare the baking dish

Preheat your oven to 375°F (190°C) with a rack in the center. Choose a 2-quart baking dish (about 8×11 inches, or a deep 9-inch square dish). Generously grease the bottom and sides with about 1 tbsp of the butter, making sure to coat the corners well. This not only prevents sticking but also helps build a rich, buttery crust around the edges of the gratin.

Step 2: Warm and season the cream mixture

In a small saucepan, combine the heavy cream, whole milk, garlic, thyme, nutmeg, Dijon mustard (if using), 1 tsp of the kosher salt, and about 1/2 tsp of the black pepper. Set over low to medium-low heat and warm gently until the mixture is steaming and just starting to show small bubbles around the edges, 3–5 minutes. Do not let it boil. Remove from the heat and let it stand while you prepare the vegetables so the flavors infuse the cream.

Step 3: Slice and dry the root vegetables

Peel the potatoes, parsnips, and carrots. Using a mandoline (carefully) or a sharp knife, slice them into thin rounds about 1/8 inch (3 mm) thick so they cook evenly and become tender at the same time. As you slice, keep the potatoes in a bowl of cold water to prevent browning, then drain and pat them very dry with a clean kitchen towel or paper towels. Dry vegetables help the cream cling and the layers cook into a cohesive gratin instead of becoming watery.

Step 4: Soften and sweeten the onions

In a medium skillet, heat 1 tbsp butter and the olive oil over medium heat. Add the sliced onion, along with a small pinch of salt, and cook, stirring occasionally, until the onion is very soft and lightly golden at the edges, about 8–10 minutes. You are not aiming for deep caramelization here, just sweetness and tenderness. Remove from the heat and set aside.

Step 5: Layer the vegetables, onions, and cheese

In a small bowl, toss together the grated Gruyère and sharp cheddar. Reserve about 3/4 cup of the cheese mixture for the topping and keep the rest for layering. To build the gratin, arrange a slightly overlapping layer of potato slices in the bottom of the buttered dish, shingling them like roof tiles. Sprinkle lightly with a pinch of the remaining salt and pepper. Add a thin scattering of sautéed onions and a small handful of the cheese. Ladle a few tablespoons of the warm cream mixture over this layer.

Repeat with a layer of parsnip slices, then carrot slices, seasoning each layer lightly with salt and pepper, adding onions and cheese, and moistening with the cream mixture as you go. Continue alternating the vegetables until you have used everything, finishing with a neat top layer of mixed root vegetables. Pour any remaining cream mixture evenly over the top and press down gently with your hands or a spatula to settle the layers and help the cream distribute.

Step 6: Make the buttery crust topping

In a small bowl, combine the breadcrumbs with the remaining 3/4 cup of grated cheese. Melt the remaining 3 tbsp butter, then pour it over the breadcrumb mixture and stir until all the crumbs are evenly coated and clump together slightly. Sprinkle this buttery crumb-and-cheese mixture evenly over the surface of the gratin, covering as much of the top as possible to form a rich, crunchy crust.

Step 7: Bake until bubbling and golden, then rest

Cover the baking dish tightly with aluminum foil, tenting it slightly so it does not stick to the topping. Bake covered for 45 minutes. Remove the foil and continue baking for 25–35 minutes more, until the vegetables are completely tender when pierced with a knife and the top is deeply golden and crisp. If you want extra color, you can broil for 1–3 minutes at the end, watching closely. Transfer the gratin to a cooling rack and let it rest for 10–15 minutes before serving; this allows the layers to set and makes slicing cleaner. Sprinkle with a few fresh thyme leaves and a tiny pinch of flaky sea salt, if you like, just before bringing it to the table.

Pro Tips

• Keep slices even: Aim for 1/8-inch (3 mm) thick slices. Thicker pieces may stay firm in the center while the top burns; thinner slices cook into a silky, cohesive texture.
• Season lightly but often: A pinch of salt and pepper on each layer creates a well-seasoned gratin without any one part tasting overly salty.
• Do not skip drying the potatoes: Excess surface moisture dilutes the cream and prevents the sauce from thickening nicely.
• Let it rest: The gratin will seem loose and bubbly right out of the oven; resting helps the cream thicken and the layers hold together when scooped.
• Cheese choice matters: Gruyère or Comté provide nutty richness. A small amount of sharp cheddar adds depth but too much can turn oily, so keep close to the suggested amounts.

Variations

• Smoky bacon or pancetta: Cook 4–6 slices of chopped bacon or pancetta until crisp. Drain well and sprinkle between layers with the onions and cheese for a smoky, savory twist.
• Herby version: Swap thyme for a mix of fresh rosemary and sage (use sparingly, as they are stronger). Add a bay leaf to the cream while it heats, then remove before assembling.
• Extra-veg gratin: Add thin slices of celery root (celeriac) or a layer of shredded Tuscan kale between the root vegetable layers for more earthiness and color.

Storage & Make-Ahead

To make ahead, assemble the gratin completely up through Step 6, cover tightly with foil, and refrigerate for up to 24 hours. When ready to bake, let it sit at room temperature for about 30 minutes while the oven preheats, then bake as directed, adding 5–10 extra minutes if needed. Leftover baked gratin keeps well in an airtight container in the refrigerator for up to 3 days. Reheat individual portions in a 350°F (175°C) oven, covered with foil, for 15–20 minutes, then uncover for the last 5 minutes to re-crisp the top. You can also reheat in a skillet over low heat with a splash of cream or milk if it seems dry.

Nutrition (per serving)

Approximate values per serving (1/6 of the recipe): 460 calories; 30 g fat (18 g saturated); 38 g carbohydrates; 6 g fiber; 9 g protein; 600 mg sodium. Actual values will vary based on the exact cheeses, cream, and vegetables used.