This luscious but lightened up Potato Leek Gratin is a delicious choice for your holiday menu. Whole milk is used in place of heavy cream to create this comforting potato side dish.
You might not instantly think of a potato gratin recipe when trying to plan a lighter holiday menu. But, with some simple modifications, you can create this utterly delicious Potato Leek Gratin that is far lighter than traditional potatoes au gratin. Sliced leeks have a mild onion flavor that intensifies when sautéed and baked into layers of thin sliced potatoes with Gruyère and Parmesan cheese.
This is a recipe that I would put on any menu, whether it was a holiday or any old day of the week, and be absolutely positive it would be well received.
The Best Potatoes to Use
I like Yukon gold potatoes best for any potato casserole including this Potato Leek Gratin. Hands down, no contest. They are creamy and buttery on their own which means you can add less butter and lighter dairy, for example whole milk instead of heavy cream, and still get a luscious result. They have also have a waxier texture than other potatoes and hold together well after baking.
Technically, Gruyere and Parmesan are not considered vegetarian cheeses because they both contain rennet. Look for vegetarian alternatives or substitute Swiss for the Gruyere and a vegetarian, plant-based hard cheese for the Parmesan.
How to Thinly Slice Potatoes
The quickest, easiest way to thinly and evenly slice potatoes is with a mandolin. Peel the thin skins before slicing.
Read and follow the manufacturer directions for your mandolin to slice your potatoes about 1/4-inch thick.
If you don’t have a mandolin, you can use your food processor with the slicing blade. For nicely shaped slices, cut the potatoes in half first and place them cut side down against the blade. If neither of these methods work for you a sharp knife and a steady hand will do. Just be sure to slice them as evenly as possible.
How to Slice Leeks
Leeks look like gigantic green onions (aka, scallions) and although they are a classic spring vegetable, you can find them all year round. They have a mild onion flavor and are delicious paired with potatoes. The edible part of the leek is the white and light green part of the long cylinder, between the stem end and dark green leafy section.
- Set the leek on a cutting board and grab a sturdy chef’s knife.
- Slice off the root end and the dark green leaves.
- Slice the remaining leek cylinder in half, lengthwise.
- Slice each half crosswise into 1/2-inch slices.
How to Clean Leeks
There is no need to wash your whole leek before slicing it. Since the leek is composed of layers, or sheaths of tightly bound leaves, it is necessary to slice it first to be sure you are ridding it of any debris that might of collected inside.
My favorite way to clean leeks is to transfer the slices to a salad spinner. Just give them a good rinse with cool water, spin them and repeat this process, spinning until dry. You can also set them in a colander and give them a good rinse, draining them well afterwards.
How to Make Potato Leek Gratin
- Sauté the leeks in a little melted butter and season with salt.
- Cook, stirring occasionally, until tender and golden brown. Remove the pan from the heat.
- Arrange half of potato slices evenly over the bottom of the prepared baking dish.
- Top with half of the leeks and sprinkle with salt.
- Scatter Gruyère cheese over the top.
- Repeat the layers layers with the remaining potatoes, leeks, salt, and Gruyère.
- Pour the milk evenly over the potato mixture.
- Sprinkle Parmesan over the top.
- Cover the pan with foil and bake until the potatoes are fork tender. Remove the foil and broil for a few minutes until golden brown.
Sprinkle the Potato Leek Gratin with a little freshly ground pepper and let it rest for about 5 minutes before serving.
Can I Make Potato Leek Gratin In Advance?
Once potatoes are sliced they will begin to oxidize and brown if not baked pretty quickly. You can, however, assemble the dish a day in advance if necessary. After assembled, press plastic wrap down on to the surface, smoothing it out to remove as much air as possible and then tightly cover the dish with a second piece of plastic wrap or foil and refrigerate it overnight. Allow the chilled Potato Gratin to rest on the kitchen counter for about 30 minutes before baking to take the chill off. The baking time may need to be increased a little. The top layer of potatoes may brown a bit but it should not be too noticeable after it is baked.
Store leftovers, covered, for up to 3 days in the refrigerator.
Potato Leek Gratin
- 3 pounds Yukon gold potatoes, peeled
- 1 large leek
- 1 tablespoon butter
- 1 ¼ teaspoons kosher salt, divided
- 1 cup shredded Gruyère cheese, about 4 ounces (see Notes below)
- 1 cup whole milk
- ¼ cup grated Parmesan cheese, about 1 ounce (see Notes below)
- ½ teaspoon freshly ground black pepper
- Preheat oven to 375 degrees F. Coat a 13- x 9-inch baking dish with nonstick cooking spray.
- Use a mandoline or a food processor with the slicing blade to thinly slice the potatoes. Set aside.
- Trim and discard the root end and dark green end from the leek. Use a sharp knife to slice the leek in half, lengthwise, to expose the center. Flip each half over, cut-side down and slice them crosswise into thin 1/2-inch slices. Place the sliced leeks in a colander or salad spinner, rinse and drain well.
- Melt the butter in a 10-inch skillet over medium heat. Add the sliced leeks and season with 1/4 teaspoon salt. Cook for 5 to 6 minutes, stirring occasionally, until tender and golden brown. Remove the pan from the heat.
- Arrange half of the potato slices evenly over the bottom of the prepared baking dish and top with half of the leeks. Sprinkle with 1/2 teaspoon salt and 1/2 cup Gruyère cheese. Repeat layers with remaining half of potatoes, remaining leeks, remaining 1/2 teaspoon salt, and remaining 1/2 cup Gruyère. Pour the milk evenly over the potato mixture and sprinkle with Parmesan.
- Cover the pan with foil and bake for 45 minutes or until the potatoes are fork tender. Remove the foil and set the oven to broil. Broil for 3 to 5 minutes or until golden brown (watch closely). Remove the pan from the oven and sprinkle with pepper. Allow to rest for 5 minutes before serving.
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Adapted from Cooking Light