Smoky Charred Leek and Potato Gratin with Gruyere Crust

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Charred Leek and Potato Gratin gets its depth from leeks blistered in a hot dry skillet before they ever meet the cream, so the smoky char comes through in every bite instead of just tasting like a plain potato bake.

I started charring the leeks after one too many gratins came out tasting flat. The extra 8 minutes in a hot pan changes the whole dish.

Thin potato slices, a garlic and thyme cream, and a gruyere top do the rest. Bake it covered first so the potatoes steam through, then uncover for a deep golden crust.

This one comes together in about 20 minutes of prep and bakes low and slow for over an hour, so it’s a good one to start while something else roasts in the oven.

Why You’ll Love This Recipe

• Charred leeks add smoky depth without extra spices
• Thin, even potato slices cook through evenly every time
• Assembles a day ahead, tastes even better the next day
• One dish feeds six for a low per-serving cost

Ingredient Notes

• Leeks: Use the white and light green parts only. Char them cut-side down in a dry skillet until the edges blacken before layering.
• Yukon gold potatoes: Their waxy texture holds shape and creaminess. Russets work too but release more starch and can turn grainy.
• Heavy cream: Full-fat cream keeps the layers from splitting during the long bake. Half-and-half works but gives a thinner sauce.
• Gruyere cheese: Melts smoothly and browns well under the broiler. Swap in sharp cheddar or comte if that’s what you have.
• Fresh thyme: Infuse it into the cream while it simmers so the flavor spreads evenly. Dried thyme works at half the amount.

Smoky Charred Leek and Potato Gratin with Gruyere Crust

Yukon gold potatoes and cast iron-charred leeks baked in garlic-thyme cream with a golden gruyere crust.

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Prep Time 20 minutes mins

Cook Time 1 hour hr 10 minutes mins

Total Time 1 hour hr 40 minutes mins

Servings: 6 servings

Course: Side Dish

Cuisine: French

Calories: 480

Ingredients Method Notes

Ingredients

  

For the Leeks and Potatoes

• 4 leeks large (about 900 g); white and light green parts only, halved lengthwise, rinsed
• 2 tbsp olive oil
• 900 g Yukon gold potatoes sliced 3mm thick
• 1 tsp kosher salt plus more to taste
• 1/2 tsp black pepper freshly ground

For the Cream

• 1 tbsp unsalted butter for greasing the dish
• 3 cloves garlic minced
• 500 ml heavy cream
• 250 ml whole milk
• 1 tbsp fresh thyme leaves only
• 1 pinch nutmeg freshly grated
• 200 g gruyere cheese grated
• 50 g parmesan cheese grated

Method

 

Char the Leeks

1. Halve leeks lengthwise, rinse any grit from between the layers, and pat dry.
2. Heat a dry cast iron skillet over medium-high heat. Add leeks cut-side down with the olive oil and cook 8 to 10 minutes until deeply charred in spots, turning once.
3. Set leeks aside to cool slightly, then roughly chop into 2-inch pieces.

Make the Cream

1. In a saucepan over medium heat, combine cream, milk, garlic, thyme, and nutmeg. Bring to a gentle simmer, about 4 to 5 minutes, then remove from heat.

Assemble and Bake

1. Heat the oven to 190 C / 375 F. Butter a 9x13 inch baking dish.
2. Layer a third of the potato slices in the dish, overlapping slightly, and season with salt and pepper. Scatter half the charred leeks over top.
3. Repeat with another layer of potatoes and the remaining leeks, then finish with a top layer of potatoes.
4. Pour the warm cream mixture evenly over the layers, pressing down gently so it seeps between the slices.
5. Scatter gruyere and parmesan over the top and cover tightly with foil.
6. Bake covered for 35 minutes. Remove the foil and bake 20 more minutes, until the top is deep golden and a knife slides through the potatoes with no resistance.
7. Rest 10 minutes before slicing and serving.

Notes

• Dry the charred leeks well before layering, excess moisture makes the gratin watery.
• Don't skip simmering the cream, it seasons the potatoes as they bake.
• Test doneness with a paring knife through the center, not just the edges.
• Use a shallow wide dish, not deep, for even cooking and more browned surface.

Tips for Success

• Slice potatoes to an even 3mm thickness with a mandoline so every layer cooks at the same rate.
• Char the leeks in a dry skillet until the cut edges blacken in spots, this builds the smoky base flavor.
• Simmer the cream with garlic and thyme for 4 to 5 minutes before pouring, this seasons every layer evenly.
• Cover the dish with foil for the first 35 minutes so the potatoes steam through before the top browns.
• Let the gratin rest 10 minutes before cutting, this lets the cream set so slices hold their shape.

Variations

• Swap gruyere for sharp cheddar and stir a spoon of dijon mustard into the cream for extra tang.
• Layer in crisp bacon lardons between the potatoes for a smoky, meaty version of this gratin.
• Use half sweet potato and half Yukon gold for a layered gratin with more color and natural sweetness.

Storage and Reheating

Charred Leek and Potato Gratin keeps well in the fridge for up to 4 days, covered tightly in the baking dish or moved to an airtight container.

Reheat individual portions in a 175 C / 350 F oven for 15 to 20 minutes, covered with foil, until warmed through. A microwave works for a single slice in a pinch, about 2 minutes, though the top won’t stay crisp.

I don’t recommend freezing this gratin. Cream sauces separate and turn grainy once potatoes thaw, and the texture goes mealy instead of creamy.

Serving Suggestions

Charred Leek and Potato Gratin works as a side to roast chicken, pan-seared steak, or a simple weeknight pork roast.

For a vegetarian dinner, serve it as the main with a lemony arugula salad and warm crusty bread on the side to mop up the cream.

Leftovers make a good lunch cold or reheated, next to a soft-boiled egg and some quick pickles.

FAQ

Why is my charred leek and potato gratin watery instead of creamy?

Usually raw potatoes release starch and water while baking, or the gratin didn’t rest long enough before cutting. Pat the charred leeks dry before layering, and let the finished gratin sit 10 minutes so the cream thickens and reabsorbs into the potatoes. If it’s still loose, bake uncovered 5 to 10 more minutes to reduce the liquid.

Can I use onions instead of leeks in this potato gratin?

Yes, sliced yellow onions work as a swap, though leeks give a milder, sweeter char than onions do. Sauté onion halves cut-side down the same way until browned and softened, about 8 minutes. Expect a slightly sharper flavor and less of the delicate leek sweetness in the final dish.

Can I assemble this charred leek and potato gratin the night before baking?

Yes, assemble it fully, cover, and refrigerate up to 24 hours before baking. Pull it out 20 minutes before it goes in the oven so it’s not ice cold, and add 5 to 10 extra minutes to the covered baking time since it’s starting cold.

What main dishes pair well with charred leek and potato gratin?

Roast chicken, seared steak, or grilled sausages all work well since the gratin is rich enough to be the standout side. A sharp green salad with a mustard vinaigrette cuts through the cream nicely. It also eats like a full meal on its own with a piece of crusty bread.

Is charred leek and potato gratin gluten free?

Yes, as written this gratin is gluten free since potatoes, leeks, cream, and cheese don’t contain gluten. Double check your cheese labels though, since some pre-shredded blends add anti-caking agents with gluten-based fillers. No flour or bread is used to thicken the cream in this version.

What’s the difference between this gratin and a classic potato gratin dauphinois?

Classic gratin dauphinois skips the charring step and usually leaves out cheese, relying on cream, garlic, and nutmeg alone. This version chars the leeks first for a smoky edge and adds gruyere and parmesan for a browned, cheesy crust. Both use thinly sliced potatoes baked low and slow.

Related recipes

• this Smoked Salmon and Leek Tart