You’ll be the gold medal holiday side dish winner with this Creamy Potato Leek Gratin that’s loaded with gruyere and parmesan cheese. Perfectly browned with crispy edges and rich, tender scalloped potatoes baked in whole milk and heavy cream. An indulgent side that’ll have your gang asking for more!
Why You’ll Love this Recipe
- What’s not to love about tender sliced potatoes baked to perfection in a creamy, cheesy sauce!
- It’s budget-friendly using basic pantry and fridge ingredients.
- You can make it ahead and reheat!
- The number of servings can be easily adjusted for small gatherings or huge feasts.
- It’s gluten-free!
Key Ingredients & Substitutions
Potatoes – I like red-skinned or Yukon gold potatoes in gratins and casseroles because they hold their shape when baked better than starchy russet potatoes.
Vegetables – Leeks and fennel go so well together and add brightness to an otherwise heavy side dish. Feel free to mix things up with mushrooms, cauliflower, zucchini or cabbage.
Cheese – I love younger gruyere cheese for its creamy, salty, nutty flavor. And the cheese melts beautifully. Aged varieties are firmer and can have a grainy texture when melted. Swiss cheese along with fontina or a mild cheddar are great substitutes.
Cream – A blend of heavy cream, or whipping cream, with whole milk is the way to go. Lighter options can curdle while baking and you'll end up with a watery gratin.
Herbs – I kept things simple by making use of the fresh fennel fronds and adding parsley directly in the dish. Thyme sprigs, tarragon, oregano and chives totally work as well.
Leeks vs. Onions
If you're not already familiar with leeks, they're in the onion family and look like giant green onions. They have a sweeter flavor than green onions and are much milder than regular onions. When leeks are cooked they take on a creamy, buttery texture. You can substitute shallots or onions for leeks but expect bolder flavor.
- Preheat & Prep – Preheat oven while you prep veggies and butter casserole dish or spray with cooking spray.
- Leek Mixture - Melt butter or heat olive oil in a large skillet over medium heat. Sauté white and light green parts of leeks until softened, 5-7 minutes. Add minced garlic cloves, cook 1 minute and set aside.
- Assembling - Arrange half of sliced fennel in an even layer in prepared baking dish and sprinkle with fresh herbs, salt and pepper. Top with half of potato slices overlapping slightly. Cover potatoes with half of leek mixture. Season generously with salt and pepper. Spread half of gruyere and grated parmesan cheese over. Repeat the layering process one more time.
- Cream Mixture - Bring whole milk and heavy cream to a soft simmer in a medium saucepan. Remove from heat and carefully pour mixture over gratin.
- Into the Oven – Bake uncovered until potatoes are very tender, liquid is almost absorbed, and the top is deep golden brown, about 60-70 minutes.
- Serve – Let gratin rest 10 minutes. Garnish with fresh herbs and enjoy!
Prepping Leeks – Use white and light green parts only so discard (or compost) coarse, dark green tops and end with roots. Halve lengthwise and give a good rinse to remove any grit hiding between the layers.
Slicing Potatoes – A handheld mandoline is an economical gadget that makes uniform slicing a breeze. But it you’re comfy using a sharp knife go for it.
Seasoning - Be sure to season each layer of potatoes with kosher salt and ground black pepper to maximize flavor.
Sauce - Stick with whole milk and heavy cream to minimize the risk of the sauce breaking.
Make Ahead when Entertaining
No need to fret over Thanksgiving or Christmas dinner! This gratin dish can be assembled and baked 3 hours before serving. Let rest on counter covered in aluminum foil. Rewarm with foil on in 375°F oven 20-30 minutes.
You can also prepare and bake the gratin 1 day ahead. Cover and refrigerate. Bring it to room temperature and bake as just mentioned until hot. Leftovers keep in the fridge for 4 to 5 days. Entertaining made easy!
With Meat – Turn the recipe into a full meal by adding browned ground pork, shredded cooked chicken or turkey, chopped ham or rendered bacon.
Make Vegan – To make the recipe vegan, substitute in whole coconut, oat or rice milk, along with a vegan cheese or omit cheese altogether.
Sweet Potatoes or Apples – Vary the dish in sweetness and flavors with interspersed sliced sweet potatoes and/or apples. Uniform slices will keep cooking time the same.
Main Dishes to Serve with au Gratin Potatoes
The options are endless when it comes to main courses this creamy gratin can accompany. Here are some favorites for a casual dinner or holiday meal.
Remember to PIN to Make the Recipe Later!
They sure can! Let them cool completely after baking. Cut into individual portions or leave uncut in casserole dish. Either way, wrap tightly with foil and freeze up to 3 months. When ready to enjoy, thaw in the refrigerator overnight or bake from frozen. Bake covered with foil at 375 degrees F until potatoes are hot and golden, 45 to 60 minutes. Double the time if potatoes are frozen.
It’s best to stick with full fat cheese, milk and cream in this recipe. Using a lower-fat variety runs a high risk of the sauce breaking while cooking and having a watery gratin. Also, if you slice the potatoes ahead and keep them in cold water so they don’t turn brown, be sure to thoroughly pat them dry.
It basically comes down to either having cheese or no cheese. Scalloped potatoes are baked in a cream sauce without any cheese. Au gratin potatoes, however, have plenty of cheese between the layers of potatoes making it a more decadent dish.
More Delicious Weeknight & Holiday Side Dishes!
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📋 Recipe Card
Creamy Potato Leek Gratin with Fennel
- 2 tablespoons butter
- 3 leeks , white and pale green parts only sliced into ¼-inch half moons
- 4 cloves garlic , minced
- 2 fennel bulbs with fronds , trimmed, cored, thinly sliced, 2 tablespoons fronds reserved
- ¼ cup fresh parsley , chopped
- 3 pounds red-skinned or yukon gold potatoes , peeled, cut into ¼-inch thick slices
- 2 cups gruyere cheese , shredded
- 1 ½ cups Parmesan cheese , freshly grated
- 1 cup whole milk
- 1 cup heavy cream
- Preheat oven to 375°F. Butter 13x9x2-inch baking dish.
- Melt 2 tablespoons butter or olive oil in large skillet over medium heat. Add leeks and cook until tender, stirring occasionally, about 7 minutes.
- Add garlic and cook 1 minute, stirring frequently. Remove from heat.
- Arrange half of sliced fennel in a even layer in prepared baking dish. Sprinkle with 1 tablespoon fennel fronds, half of the parsley, and season with salt and pepper.
- Arrange half of sliced potatoes overlapping slightly on top of the fennel and herbs. Top potatoes with half of leek mixture. Sprinkle generously with salt and pepper. Spread half of gruyere and grated parmesan cheese over.
- Repeat layering with remaining fennel, herbs, potatoes, leek mixture, and cheeses. Sprinkle assembled gratin with salt and pepper.
- Bring whole milk and heavy cream to a simmer in a small saucepan. Pour mixture over gratin.
- Bake uncovered until vegetables are very tender, liquid is almost absorbed and top is deep golden brown, about 1 hour to 1 hour 10 minutes.
- Let gratin rest 10 minutes before serving. Garnish with extra fennel fronds and parsley. Enjoy!
- Prepping Leeks – Use white and light green parts only Halve lengthwise and rinse to remove any hiding grit between the layers.
- Slicing Potatoes – A handheld mandoline is an economical gadget that makes uniform slicing a breeze, or use a sharp knife.
- Seasoning - Be sure to season each layer of potatoes with kosher salt and ground black pepper to maximize flavor.
- Sauce - Stick with whole milk and heavy cream to minimize the risk of the sauce breaking.
- If halving the recipe, use an 8x8 or 9x9 casserole dish.
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