The moment you take a bite of this rich, creamy potato leek au gratin, you'll wonder why you ever settled for plain mashed potatoes. Thin slices of potatoes and leeks are layered with a flavorful cream sauce and a cheesy golden brown crust. It's an effortless side dish with only 15 minutes of hands-on time!
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I have never met anyone who didn't fall in love with this potato casserole. Every time I make it, it’s gone before I can even get a second helping.
It's the ultimate elevated comfort food and I often serve it at easter with roasted watermelon radishes. It pairs wonderfully with lamb steaks, but also roast chicken and sous vide mustard pork.
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📖Why My Recipe Works
The leeks are cooked in butter, and the potatoes are tossed in herbs and seasonings, so they're packed with flavor even before they hit the baking dish.
🧾Ingredient Notes
- Potatoes- The best potatoes to use are Yukon gold potatoes for their buttery texture. But you can also use Russet or red potatoes.
- Leeks- You'll need one large leek or two medium leeks.
- Butter- If using salted butter, slightly reduce the salt in this recipe.
- Heavy Cream- You can also use half and half or whole milk with a little bit of cornstarch.
- Cheese- Shredded emmental, Swiss, or gruyère cheese will also work well.
- Ground Nutmeg- A little goes a long way. If you don't have nutmeg, you can skip or use allspice or white pepper instead.
- Fresh Thyme- Swap with ½ teaspoon dried thyme. You can also use fresh rosemary or sage.
⏲️How to Make Potato Leek Gratin
- Slice the leeks into rings, then soak them in a bowl with water to remove all the dirt. Drain and pat dry before cooking.
- In a skillet over medium heat, melt butter and cook the leeks until soft and translucent. They should still be bright in color and hold their shape.
- Use a knife or mandoline to slice the potatoes thinly. I prefer to leave the skins on for more texture.
- Toss the potato slices with salt, pepper, nutmeg, and thyme to evenly coat them before layering.
- Arrange the potatoes in a single layer in a baking dish. Then, spread the leeks on top. Repeat with the second layer.
- Sauté the garlic on the same pan where you cooked the leeks. Add heavy cream and mustard and let it simmer for 3-4 minutes until thick and warm.
- Pour the cream over and gently tilt the baking dish a few times to help the sauce distribute evenly throughout. Generously sprinkle a layer of cheese on top.
- Cover with foil and bake until the potatoes are tender, about 35 minutes. Then, increase the temperature to 425F, uncover, and bake for 20 more minutes or until cheese is bubbly and golden.
👩🏻🍳 Expert Tips
- Let the heavy cream sit at room temperature for 10-15 minutes before cooking to prevent curdling.
- Slightly overlapping the potato slices helps them cook evenly and prevents dry spots.
More Potato Recipes
🌡️Make Ahead and Storing Leftovers
You can assemble the gratin a day in advance, cover with foil, and refrigerate. When ready to serve, bake as instructed.
To store leftovers, transfer to an airtight container or cover tightly with foil. Store it in the fridge for up to 4 days. Reheat in the oven at 350F for 15-20 minutes, covered with foil to prevent drying out.
Add A Flavorful Twist
To switch things up, you can toss in some rutabaga or carrots. You can also sauté some mushrooms with the leeks. For toppings, you can add crispy bacon bits for more crunch. And if you like a little heat, a pinch of red pepper flakes or cayenne will do the trick.
Did you enjoy making this recipe? Show it some love with ⭐⭐⭐⭐⭐ and leave a comment! Hungry for more FLAVORFUL recipes?
📖 Recipe Card
Leek and Potato Gratin
Ingredients
- 1 large leeks trimmed and halved lengthwise
- 2 tablespoons unsalted butter plus more for the pan
- 1 ½ pounds potatoes Yukon gold
- 1 teaspoon kosher salt
- ½ teaspoon black pepper
- ¼ teaspoon freshly ground nutmeg
- 1 Tablespoons minced fresh thyme leaves
- 2 cloves garlic finely chopped
- 1 cup heavy cream
- 1 Tablespoon Dijon mustard
- ¾ cup grated Emmental cheese swiss or gruyere
Instructions
- Preheat oven to 350 degrees. Butter a 2-quart baking dish.
- Trim the leeks and cut into thin rings. Rinse thoroughly to remove all the grit. Melt butter in a skillet over medium heat. Add leeks, and cook until translucent, 3 to 4 minutes.2 tablespoons unsalted butter, 1 large leeks
- Peel your potatoes and slice them into thin slices with either a mandolin or a knife. Toss the potatoes with salt, pepper, nutmeg, and thyme leaves.1 ½ pounds potatoes, 1 teaspoon kosher salt, ½ teaspoon black pepper, ¼ teaspoon freshly ground nutmeg, 1 Tablespoons minced fresh thyme leaves
- Arrange ½ of the potatoes in dish, slightly overlapping slices. Spread the leeks on top. Repeat with the second layer.
- In the same pan the looks were in add the garlic and sauté for 1 minute over medium-low heat. Add the cream and the mustard. Simmer for 3 to 4 minutes.1 cup heavy cream, 2 cloves garlic, 1 Tablespoon Dijon mustard
- Pour the cream over the leeks and potatoes and top with the cheese. Cover with aluminum foil and transfer to the oven. Bake for 35 minutes.¾ cup grated Emmental cheese
- Increase temperature to 425 degrees, uncover and bake until the cheese is bubbling and golden, 15 to 20 minutes longer. Let cool slightly before serving.
Notes
- This is a relatively small batch potato recipe serving 4 to 6 people. This recipe can be easily doubled or tripled for larger gatherings.
Equipment
- Baking dish
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