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Potato and Leek Gratin with Gruyere, fall casserole recipes comfort
Brittany Stage

Potato and Leek Gratin with Gruyere

Thinly sliced Yukon Gold potatoes and tender leeks layer with a creamy Gruyere sauce for a fall side dish that looks impressive but follows a straightforward process. It serves eight and pairs well with almost any roasted or grilled protein.
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Prep Time 25 minutes
Cook Time 1 hour 10 minutes
Total Time 1 hour 35 minutes
Servings: 8 servings
Course: Side Dish
Cuisine: American
Calories: 380
Ingredients Equipment Method Notes

Ingredients
  

  • 3 lbs Yukon Gold potatoes peeled and sliced 1/8-inch thin, about 6 medium potatoes
  • 3 medium leeks white and light green parts only, halved lengthwise and sliced into 1/4-inch half-moons
  • 2 cups Gruyere cheese shredded, divided, about 6 oz
  • 2 cups heavy cream
  • 3 cloves garlic minced
  • 2 tbsp unsalted butter
  • 1 tbsp all-purpose flour
  • 1 tsp kosher salt
  • 1/2 tsp black pepper
  • 1/4 tsp freshly grated nutmeg
  • 1 tsp fresh thyme leaves or 1/2 tsp dried thyme

Equipment

  • 2-quart baking dish or 9x13 inch baking dish
  • mandoline or sharp knife
  • medium saucepan
  • whisk
  • cutting board

Method
 

  1. Preheat your oven to 375 degrees F. Butter the bottom and sides of your baking dish generously and set it aside.
  2. Rinse the sliced leeks thoroughly in a bowl of cold water. Leeks trap dirt between their layers, so swish them around and let the grit sink to the bottom, then lift the leeks out with your hands and pat them dry. Set aside.
  3. Make the Gruyere cream sauce. Melt the butter in a medium saucepan over medium heat. Add the minced garlic and cook for 30 seconds until fragrant, stirring constantly so it does not brown. Whisk in the flour and cook for 1 minute. Slowly pour in the heavy cream while whisking to keep the sauce smooth. Add the salt, pepper, nutmeg, and thyme. Cook, stirring frequently, for 3 to 4 minutes until the sauce thickens enough to coat the back of a spoon. Remove from heat and stir in 1 cup of the shredded Gruyere until melted and smooth.
  4. Build the gratin in layers. Arrange one third of the potato slices in overlapping rows on the bottom of the prepared baking dish. Top with half of the sliced leeks and spoon about one third of the cream sauce over the top. Repeat with another layer of potatoes, the remaining leeks, and another third of the sauce. Finish with the last layer of potato slices and pour the remaining sauce evenly over the top. Press the entire layered dish firmly down with your palm. This compacts the layers so they bake evenly and the gratin holds its shape when you cut into it.
  5. Cover the baking dish tightly with aluminum foil. Bake covered for 45 minutes. The potatoes should be mostly tender at this point. Test by inserting a thin knife into the center. It should meet only a little resistance.
  6. Remove the foil and scatter the remaining 1 cup of Gruyere evenly over the top. Return the dish to the oven uncovered and bake for an additional 20 to 25 minutes until the top is deep golden brown and bubbling at the edges. The surface should look set, not wobbly.
  7. Remove from the oven and let the gratin rest for at least 10 minutes before cutting and serving. Resting allows the cream sauce to firm up so you can cut clean, neat squares. It will hold at room temperature for up to 1 hour without losing quality.

Notes

Use a mandoline to get the potato slices consistently thin. Uneven slices mean some layers will be overcooked while others are still firm. If you do not have a mandoline, use your sharpest knife and take your time. Consistent thickness is the most important technique in this recipe.