Potato and Leek Gratin with Gruyere

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This potato and leek gratin is the dish I pull out when I need a side that looks like I tried harder than I did. The active work is about 25 minutes: slicing potatoes, cleaning leeks, and making a quick cream sauce on the stove. After that the oven does 70 minutes of work while you deal with everything else on the table.

Leeks need a proper rinse. They trap grit between every layer, and if you skip that step you will absolutely taste sand in the finished dish. Halve them, slice them, then swish them in a bowl of cold water and lift them out by hand. Takes two minutes and it matters.

The gratin serves eight as a side and holds at room temperature for up to an hour without losing anything, which makes it genuinely useful for holidays or any dinner where the main protein needs your full attention at the end.

Why you will love this

• The Gruyere cream sauce comes together in one saucepan in about five minutes and does not require any fancy technique.
• Yukon Golds hold their shape through a long bake, so the layers stay distinct instead of turning to mush.
• Pressing the layers down before baking is a small step that makes a real difference: the gratin cuts into clean squares instead of sliding apart.
• It can be fully assembled the night before and refrigerated unbaked, which is one less thing to do on a busy cooking day.
• Leftovers reheat well from the oven, and the texture on day two is nearly as good as day one.

Tips for success

• Slice the potatoes to an even 1/8-inch thickness. Uneven slices mean some layers finish cooking before others. A mandoline is the fastest way to get consistency, but a sharp knife and patience work too.
• Do not rush the cream sauce off the heat. It needs 3 to 4 minutes of stirring to thicken enough to coat a spoon. If it goes into the dish too thin, the gratin can turn watery.
• Press the entire assembled dish firmly down with your palm before it goes in the oven. It feels odd but it compacts the layers so they bake through evenly and the gratin holds its shape when you cut it.
• Let it rest a full 10 minutes after it comes out. I have cut into it too early more than once and watched the sauce run everywhere. The rest time is not optional.

What to serve with it

• Roasted chicken or pork tenderloin are the most straightforward pairings. The richness of the gratin balances well against something simply seasoned.
• A bitter green salad, arugula or radicchio, cuts through the cream sauce better than a mild lettuce would.
• For a vegetarian dinner, serve it alongside roasted mushrooms or a simple tomato braise.
• Leftover gratin reheats well enough to serve alongside fried eggs the next morning, which two of my kids specifically request.

Substitutions

Gruyere is worth seeking out for its melt and nutty flavor, but fontina or a mild Swiss cheese work as a straight swap. Russet potatoes can replace Yukon Golds in a pinch, though they hold less moisture and the texture will be a little drier. Half-and-half in place of heavy cream gives you a lighter result, though the sauce will be thinner going into the dish.

If leeks are not available, shallots give a sharper onion flavor and work well in the same quantity. For a dairy-free version, the texture and flavor change significantly enough that it becomes a different dish, so I would not try to swap the cream and cheese here.

Make-ahead and storage

You can assemble the entire gratin through the layering step, cover it tightly with plastic wrap, and refrigerate it unbaked for up to 24 hours. When you bake it straight from the fridge, add about 10 minutes to the covered baking time. Store leftovers covered in the refrigerator for up to 4 days.

To reheat, cover the dish with foil and warm it in a 350-degree oven for 15 to 20 minutes. Individual portions can go in the microwave, but the oven gives you a much better texture. I do not recommend freezing this one. The cream sauce tends to separate and the potato texture suffers after thawing.

Brittany Stage

Potato and Leek Gratin with Gruyere

Thinly sliced Yukon Gold potatoes and tender leeks layer with a creamy Gruyere sauce for a fall side dish that looks impressive but follows a straightforward process. It serves eight and pairs well with almost any roasted or grilled protein.

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Prep Time 25 minutes mins

Cook Time 1 hour hr 10 minutes mins

Total Time 1 hour hr 35 minutes mins

Servings: 8 servings

Course: Side Dish

Cuisine: American

Calories: 380

Ingredients Equipment Method Notes

Ingredients

  

• 3 lbs Yukon Gold potatoes peeled and sliced 1/8-inch thin, about 6 medium potatoes
• 3 medium leeks white and light green parts only, halved lengthwise and sliced into 1/4-inch half-moons
• 2 cups Gruyere cheese shredded, divided, about 6 oz
• 2 cups heavy cream
• 3 cloves garlic minced
• 2 tbsp unsalted butter
• 1 tbsp all-purpose flour
• 1 tsp kosher salt
• 1/2 tsp black pepper
• 1/4 tsp freshly grated nutmeg
• 1 tsp fresh thyme leaves or 1/2 tsp dried thyme

Equipment

• 2-quart baking dish or 9×13 inch baking dish
• mandoline or sharp knife
• medium saucepan
• whisk
• cutting board

Method

 

1. Preheat your oven to 375 degrees F. Butter the bottom and sides of your baking dish generously and set it aside.
2. Rinse the sliced leeks thoroughly in a bowl of cold water. Leeks trap dirt between their layers, so swish them around and let the grit sink to the bottom, then lift the leeks out with your hands and pat them dry. Set aside.
3. Make the Gruyere cream sauce. Melt the butter in a medium saucepan over medium heat. Add the minced garlic and cook for 30 seconds until fragrant, stirring constantly so it does not brown. Whisk in the flour and cook for 1 minute. Slowly pour in the heavy cream while whisking to keep the sauce smooth. Add the salt, pepper, nutmeg, and thyme. Cook, stirring frequently, for 3 to 4 minutes until the sauce thickens enough to coat the back of a spoon. Remove from heat and stir in 1 cup of the shredded Gruyere until melted and smooth.
4. Build the gratin in layers. Arrange one third of the potato slices in overlapping rows on the bottom of the prepared baking dish. Top with half of the sliced leeks and spoon about one third of the cream sauce over the top. Repeat with another layer of potatoes, the remaining leeks, and another third of the sauce. Finish with the last layer of potato slices and pour the remaining sauce evenly over the top. Press the entire layered dish firmly down with your palm. This compacts the layers so they bake evenly and the gratin holds its shape when you cut into it.
5. Cover the baking dish tightly with aluminum foil. Bake covered for 45 minutes. The potatoes should be mostly tender at this point. Test by inserting a thin knife into the center. It should meet only a little resistance.
6. Remove the foil and scatter the remaining 1 cup of Gruyere evenly over the top. Return the dish to the oven uncovered and bake for an additional 20 to 25 minutes until the top is deep golden brown and bubbling at the edges. The surface should look set, not wobbly.
7. Remove from the oven and let the gratin rest for at least 10 minutes before cutting and serving. Resting allows the cream sauce to firm up so you can cut clean, neat squares. It will hold at room temperature for up to 1 hour without losing quality.

Notes

Use a mandoline to get the potato slices consistently thin. Uneven slices mean some layers will be overcooked while others are still firm. If you do not have a mandoline, use your sharpest knife and take your time. Consistent thickness is the most important technique in this recipe.

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