Baked Leek Gratin is the quintessential holiday side dish that perfectly complements slow-cooker spiral ham or roast leg of lamb with its creamy, cheesy layers and tender leeks. It’s easy to prepare, can be made in advance, and consistently earns rave reviews from guests. The ideal side dish!
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The Ingredients
This flavorful gratin is especially perfect for Easter or Mother’s Day when leeks are in season, but its rich, comforting flavors make it a delightful choice any time of the year. Find ingredient notes (including substitutions and variations) below.
Substitutions and Variations
- Vegetables – Leeks can be substituted with shallots or green onions for a stronger onion flavor, while fennel can also be used, imparting a subtle anise or licorice taste to the dish.
- Dairy – Using unsalted butter is ideal for this dish as it allows you to control the sodium content in the dish. Additionally, heavy cream or half-and-half can be used in place of whole milk, while Gruyère can be substituted with Swiss, fontina, or Emmental cheeses.
- Flavor Enhancers – Fresh lemon juice brings a vibrant brightness that should not be overlooked, while a hint of cayenne enhances the dish’s depth of flavor without overwhelming it with spice.
- A Crunchy Topping – Fresh breadcrumbs or Panko breadcrumbs, when mixed with melted butter, become wonderfully crunchy when baked, providing the perfect contrast to the creamy filling of the gratin.
See the recipe card (with video) below for a full list of ingredients and measurements.
Expert Tip:
It will seem like you have a huge amount of leeks when you add them to your large skillet. They will cook down significantly after they sauté. This is similar to how basil cooks down for spaghetti with homemade pesto and how spinach cooks down for creamy chicken florentine.
How To Make Baked Leek Gratin
- Step 1: Sauté the leeks and shallots in butter in a skillet over medium heat. Season with salt and pepper. Set aside.
- Step 2: In a clean skillet, melt butter and stir in the flour to create a roux. Cook, stirring often, for about 2 minutes.
- Step 3: Whisk in the milk, lemon juice, and seasonings. Stir until thickened, usually about 4 minutes.
- Step 4: Turn off the heat and stir the leek/shallot mixture into the thickened cream. Stir until combined. Transfer to baking dish.
- Step 5: In a medium bowl, combine 2 tablespoon melted butter with the breadcrumbs. Work the butter in with your fingers.
- Step 6: Sprinkle the breadcrumbs over the top of the gratin and bake at 400°F until golden, about 25 minutes.
How to Serve
- You’ll want the breadcrumb topping to brown lightly before removing it from the oven. If you want the topping a little more browned and crunchy, turn the broiler on HIGH and allow the gratin to bake for another minute, or two.
- This dish is very hot when it comes out of the oven. It should rest for at least 5 to 10 minutes. However, you can also cover it and let it rest for up to 30 minutes while you finish the rest of the dishes. It will stay warm.
- Though this dish is best served shortly after being removed from the oven, leftovers are delicious, too.
- In addition to a glazed holiday ham, you’ll want to be sure to have homemade dinner rolls for the perfect holiday feast.
Expert Tip:
To make amazing breadcrumbs, set 1 to 2 slices of Italian bread out for a few hours to dry out. Use a sharp knife to remove the crusts and then process in your food processor until fine. Toss with melted butter and then top the gratin.
Frequently Asked Questions
Absolutely! Assemble up to 24 hours in advance, but, don’t add the breadcrumbs until just before baking.
They are somewhere between a yellow onion and a scallion. There is an onion flavor, but the creamy filling tones down the flavor considerably. However, if you are serving anyone who despises onions, you may want to consider a different dish.
Leeks grow in the dirt, and because of their layers, there will almost always be dirt in the center of the vegetable. After cutting them up, run them under cool water in a colander and then dry them with paper towels.
Other Amazing Side Dishes
Ready to make the best side dish in town? Go for it!
And when you do, be sure to take a photo of it, post it on Instagram, and tag @HowToFeedaLoon and hashtag #HowToFeedaLoon!
Baked Leek Gratin
Video
Equipment
- 1 1-quart baking dish smaller than a 9×13"
Ingredients
- 8 tablespoon unsalted butter divided
- 5 to 6 leeks washed, sliced, and roughly chopped, use mostly the white parts and some of the green.
- 1 large shallots chopped
- Salt and pepper
- 3 tablespoon all-purpose flour
- 2 cups whole milk
- ½ teaspoon cayenne pepper
- 1 tablespoon lemon juice
- 1 cup Gruyére cheese grated
- ⅔ cup fresh bread crumbs See NOTES
Instructions
- Preheat oven to 400°F.
- In a large skillet (12"), melt 3 tablespoon butter over medium heat. Add the leeks and shallots, and cook, stirring often, until softened and starting to lightly brown, about 15 minutes. Stir in 1 teaspoon salt and ½ teaspoon black pepper.8 tablespoon unsalted butter, 5 to 6 leeks, 1 large shallots, Salt and pepper
- Either use a new skillet or transfer the sautéed leeks to a bowl and clean out the skillet with a damp paper towel.
- Heat 3 tablespoon butter over medium heat until melted. Whisk in the flour and stir until completely combined and cook, stirring often, for 1 minute.3 tablespoon all-purpose flour
- Whisk in the milk and stir until almost all lumps are no longer visible. Stir in the cayenne, lemon juice, ¾ teaspoon salt, and ½ teaspoon black pepper. Stir until thickened, about 3 to 4 minutes. The consistency should be like gravy, but not too thick.2 cups whole milk, ½ teaspoon cayenne pepper, 1 tablespoon lemon juice
- Turn off the heat and stir in the leek mixture. Stir until combined. Transfer to the baking dish and top with the grated cheese.1 cup Gruyére cheese
- Toss the breadcrumbs with the remaining 2 tablespoon butter (melted).⅔ cup fresh bread crumbs
- Bake until bubbly and slightly golden on top, about 25 to 30 minutes. Remove from oven and let rest for 5 to 10 minutes before serving. (Or, cover with foil, and let rest for up to 30 minutes).
Christi says
This was absolutely delicious!! My whole family loved it and devoured it all! Thank you so much for sharing the recipe!!
Kris Longwell says
Hi Christi! Sorry for the late reply! We are THRILLED you made the leek gratin and the family loved it! Thanks makes us so happy! Thank you so so much for sharing and for the wonderful review. That means the world to us! Please stay in touch!! Kris & Wesley
Mimi Rippee says
This fabulous! I love leeks and they’re so under appreciated, I think. A gratin is perfect for them.
Kris Longwell says
Hi Mimi! We completely agree! We knew we wanted to come up with something featuring leeks, and finally decided a gratin was be a yummy dish. And we think it’s really so good and a perfect holiday side dish. Happy Easter!!! xoxo