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Creamy Leek and Potato Gratin with Gruyere and Thyme

Creamy leek and potato gratin layers tender Yukon Gold potatoes and softened leeks in a thyme-scented cream sauce. It bakes under foil until tender, then uncovered until the Gruyere topping is golden and bubbling.
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Prep Time 25 minutes
Cook Time 1 hour 20 minutes
resting 15 minutes
Total Time 2 hours
Servings: 8 servings
Course: Side Dish
Cuisine: French
Calories: 375
Ingredients Equipment Method Notes

Ingredients
  

For the gratin
  • 1 tbsp unsalted butter divided
  • 2 leeks medium; white and light green parts only, thinly sliced and thoroughly rinsed
  • 2 lb Yukon Gold potatoes peeled and sliced 1/8 inch thick
  • 1.5 cup heavy cream
  • 1 cup whole milk
  • 2 cloves garlic minced
  • 1 tsp fresh thyme leaves
  • 1 tsp kosher salt
  • 0.25 tsp black pepper
  • 0.125 tsp ground nutmeg
For the topping
  • 6 oz Gruyere cheese shredded (about 1 1/2 cups)

Equipment

  • 1 9x13 inch baking dish

Method
 

Prepare the gratin
  1. Heat the oven to 375°F.
  2. Grease a 9x13-inch baking dish with 1 teaspoon of the butter.
  3. Melt the remaining 2 teaspoons butter in a large skillet over medium heat.
  4. Add the leeks and cook for 6 to 8 minutes, stirring occasionally, until softened.
  5. In a medium saucepan, combine the heavy cream, milk, garlic, thyme, salt, pepper, and nutmeg.
  6. Warm the cream mixture over medium-low heat until steaming, then remove from the heat.
  7. Arrange half the potatoes in the prepared dish, spread the leeks over them, and layer the remaining potatoes on top.
  8. Pour the warm cream mixture evenly over the potatoes.
  9. Cover the dish tightly with foil and bake for 45 to 55 minutes, until a knife slides easily into the center potatoes.
Finish and bake
  1. Remove the foil and sprinkle the Gruyere evenly over the top.
  2. Bake uncovered for 20 to 25 minutes, until the cheese is golden and bubbling.
  3. Let the gratin rest for 15 minutes before serving.

Notes

For even cooking, slice the potatoes uniformly and rinse the leeks thoroughly. Refrigerate leftovers for 3 to 4 days; freezing is not recommended because the cream sauce may separate. For a lighter option, replace some of the heavy cream with whole milk.