Creamy Potato and Leek Gratin

A luxurious French-style gratin combining tender sliced potatoes and leeks in a rich cream sauce, flavored with fresh thyme. This comforting dish features layers of thinly sliced russet potatoes and buttery leeks baked until golden and bubbling.

8 servings

2 hr 12 min

Published October 4, 2025

Ingredients

•9 whole medium leeks
•3 Tbsp unsalted butter
•2 lb russet potatoes
•1½ cups heavy cream
•1 cup whole milk
•2 tsp thyme leaves
•1 piece adjustable-blade slicer

Cooking Instructions

1.
Preheat oven to 400°F with rack in middle. Generously butter a 3-qt shallow baking dish. Cut a round of parchment paper to fit just inside a 12-inch heavy skillet, then set parchment aside.
5 min
2.
Halve leeks lengthwise, then cut crosswise into 1 1/2-inch pieces (you should have about 8 cups). Wash leeks.
10 min
3.
Cook leeks in butter with 1/2 tsp salt and 1/4 tsp pepper, covered with parchment round, in skillet over medium heat, stirring occasionally, until tender, 10 to 12 minutes.
12 min
4.
Meanwhile, peel potatoes and slice crosswise 1/16 inch thick with slicer. Transfer to a large heavy pot with cream, milk, thyme, 1 tsp salt, and 1/2 tsp pepper and bring to a boil over medium heat, stirring occasionally (liquid will thicken). Stir in leeks, then transfer to baking dish.
15 min
5.
Bake, uncovered, until potatoes are tender, 45 minutes to 1 hour. Let stand 10 minutes before serving.
60 min
6.
Gratin can be baked 2 days ahead and chilled. Let stand at room temperature 30 minutes, then reheat, covered, in a 350°F oven until hot, about 30 minutes.
30 min

Cooking Instructions

Preheat oven to 400°F with rack in middle. Generously butter a 3-qt shallow baking dish. Cut a round of parchment paper to fit just inside a 12-inch heavy skillet, then set parchment aside.

5 min

Halve leeks lengthwise, then cut crosswise into 1 1/2-inch pieces (you should have about 8 cups). Wash leeks.

10 min

Cook leeks in butter with 1/2 tsp salt and 1/4 tsp pepper, covered with parchment round, in skillet over medium heat, stirring occasionally, until tender, 10 to 12 minutes.

12 min

Meanwhile, peel potatoes and slice crosswise 1/16 inch thick with slicer. Transfer to a large heavy pot with cream, milk, thyme, 1 tsp salt, and 1/2 tsp pepper and bring to a boil over medium heat, stirring occasionally (liquid will thicken). Stir in leeks, then transfer to baking dish.

15 min

Bake, uncovered, until potatoes are tender, 45 minutes to 1 hour. Let stand 10 minutes before serving.

60 min

Gratin can be baked 2 days ahead and chilled. Let stand at room temperature 30 minutes, then reheat, covered, in a 350°F oven until hot, about 30 minutes.

30 min