Easy Potato and Leek Gratin with Creamy Gruyère Sauce

There’s something so comforting about creamy potatoes layered with soft leeks and melty cheese. This one is a favorite side dish for cozy dinners or a holiday table, especially when you want to level up from classic mashed potatoes. I love this dish because it makes you feel really fancy in the kitchen but it’s really as easy as pouring cream over sliced potatoes.

To start, I slice up some starchy potatoes into thin rounds, about an eighth of an inch thick. A mandoline makes this fast and keeps the slices even, but a sharp knife works too. If you use a mandoline, please protect your hands with cut resistant gloves too. Be sure to keep them in a bowl of cold water if you slice them ahead of time so they don’t turn brown. I also prep my leek, onion, and garlic. Only use the white and light green parts of the leek (the dark green ends can be fibrous). Rinse well between the layers since leeks love to hide sandy dirt inside.

In a big pan, I melt some butter and sauté the diced onion and sliced leek over medium-low heat until they’re soft and just starting to caramelize. If they start to brown too fast, lower the heat and give them time to get sweet and tender. Toward the end, I toss in some minced garlic so it softens without burning.

Meanwhile, I warm up the cream and milk in a small pot with the other half of the garlic, a bay leaf, thyme sprigs, salt, and pepper. Letting the cream mixture gently infuse gives a deeper flavor that really makes this dish stand out. Don’t let it boil, you just want it warm and fragrant. Strain out the herbs before using.

Once everything is soft and scented, I toss the potato slices in with the leek mix to coat them evenly and season again with a bit of salt. This makes sure every bite has flavor, not just the top.

When it comes time to assemble, I butter a casserole dish and layer the potatoes in a slightly staggered pattern, like stacked cards. This helps the creamy mixture seep down into all the layers.

I pour that warm herb-infused cream right over the top and sprinkle on some shredded Gruyère cheese. If you’re looking for a great casserole dish, I love this one linked here (affiliate link). It heats evenly and always looks nice for serving too.

The dish bakes covered with foil to steam the potatoes until they’re totally tender. To finish, I take off the cover, add the rest of the cheese along with some Parmesan, and broil until it’s beautifully golden. Let it sit for a few minutes before digging in. It’s rich, cheesy, and the crowd will love it.

Tips for the Best Potato and Leek Gratin

• Use starchy potatoes like Russets or Yukon Golds for the creamiest texture.
• Slice the potatoes thin and evenly for proper cooking. A mandoline is the easiest way to do this.
• Let the gratin rest for at least 10 minutes before serving so the sauce thickens and sets.

Easy Potato and Leek Gratin with Creamy Gruyère Sauce

Level up your side dish game with this creamy potato and leek gratin baked in herb-infused cream and topped with melted Gruyère. Perfect for holidays or weeknight comfort food.

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Prep Time 25 minutes mins

Cook Time 1 hour hr 30 minutes mins

Total Time 1 hour hr 55 minutes mins

Servings: 4 -6

Course: Side Dish

Cuisine: American

Ingredients Method Video Notes

Ingredients

  

• 2.5 lb starchy potatoes peeled and sliced 1/8 inch thick
• 1 leek thinly sliced (dark green parts removed)
• 1 yellow onion diced
• 5 garlic cloves minced
• 2 tbsp butter
• 1 bay leaf
• 2 thyme sprigs
• Pinch of nutmeg
• 1 1/2 cups Gruyère cheese shredded
• 1 cup cream
• 1/2 cup milk
• 2 tbsp Parmesan cheese grated
• 1.5 tsp salt divided
• 1/2 tsp pepper

Notes

For Doubling:

• The trickiest part for me was figuring out the size of the casserole dish. I doubled this and used a 10.5″ X 7.5 casserole dish and the potatoes fit perfectly but the cream was overflowing. Because of this, I reduced the total cream amount by 1/2 cup when doubling. 
• A slightly larger casserole dish might work better, but you do want the potatoes to be crowded together in a staggered fashion. If you use a large casserole dish, you may need to add more potatoes to completely fill it. 

 

Method

 

1. In a large skillet, cook onion and leek in butter over medium-low heat until soft and lightly golden. Add half of the garlic and cook for 2 to 3 more minutes.
2. In a small saucepan, heat cream, milk, remaining garlic, bay leaf, thyme, 1 tsp salt, and pepper for 5 minutes over low heat to infuse. Remove herbs and set aside.
3. Toss potato slices with the leek mixture and season with 1/2 tsp salt and a pinch of nutmeg.
4. Butter a small casserole dish. Layer potatoes in a slightly staggered way to create spaces for the cream to seep in. Make sure you fill the whole casserole dish so the potatoes completely fill it. (see note)
5. Pour the warm cream mixture over the potatoes. Sprinkle with half of the Gruyère and cover with foil.
6. Bake at 325°F for 75 to 90 minutes, or until potatoes are tender.
7. Uncover, top with remaining Gruyère and grated Parmesan, and broil until golden and bubbly.
8. Let rest for 10 to 15 minutes before serving.

Video

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