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An overhead view of a baking dish filled with a baked leeks gratin with a portion of the casserole missing with a serving spoon in the side.

Baked Leek Gratin

Course: Side Dish
Cuisine: American / French
Prep Time: 20 minutes
Cook Time: 50 minutes
Resting Time: 10 minutes
Total Time: 1 hour 20 minutes
Servings: 6
Calories: 336kcal
Author: Kris Longwell
This dish is the perfect side, especially for a "special occasion" feast such as Easter, Mother's Day, or even Sunday dinner. It may feel like you are starting with too many leeks, but, don't worry, they cook down fairly quickly. The dish can even be prepared almost completely in advance! (See Notes).
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Equipment

  • 1 1-quart baking dish smaller than a 9x13"

Ingredients

  • 8 tablespoon unsalted butter divided
  • 5 to 6 leeks washed, sliced, and roughly chopped, use mostly the white parts and some of the green.
  • 1 large shallots chopped
  • Salt and pepper
  • 3 tablespoon all-purpose flour
  • 2 cups whole milk
  • ½ teaspoon cayenne pepper
  • 1 tablespoon lemon juice
  • 1 cup Gruyére cheese grated
  • ⅔ cup fresh bread crumbs See NOTES

Instructions

  • Preheat oven to 400°F.
  • In a large skillet (12"), melt 3 tablespoon butter over medium heat. Add the leeks and shallots, and cook, stirring often, until softened and starting to lightly brown, about 15 minutes. Stir in 1 teaspoon salt and ½ teaspoon black pepper.
    8 tablespoon unsalted butter, 5 to 6 leeks, 1 large shallots, Salt and pepper
  • Either use a new skillet or transfer the sautéed leeks to a bowl and clean out the skillet with a damp paper towel.
  • Heat 3 tablespoon butter over medium heat until melted. Whisk in the flour and stir until completely combined and cook, stirring often, for 1 minute.
    3 tablespoon all-purpose flour
  • Whisk in the milk and stir until almost all lumps are no longer visible. Stir in the cayenne, lemon juice, ¾ teaspoon salt, and ½ teaspoon black pepper. Stir until thickened, about 3 to 4 minutes. The consistency should be like gravy, but not too thick.
    2 cups whole milk, ½ teaspoon cayenne pepper, 1 tablespoon lemon juice
  • Turn off the heat and stir in the leek mixture. Stir until combined. Transfer to the baking dish and top with the grated cheese.
    1 cup Gruyére cheese
  • Toss the breadcrumbs with the remaining 2 tablespoon butter (melted).
    ⅔ cup fresh bread crumbs
  • Bake until bubbly and slightly golden on top, about 25 to 30 minutes. Remove from oven and let rest for 5 to 10 minutes before serving. (Or, cover with foil, and let rest for up to 30 minutes).

Video

Notes

NOTE: Watch the video near the top of the recipe for visual guidance.
To make fresh breadcrumbs, place 1 to 2 pieces of bread (preferably Italian or French) out on the counter for several hours, or up to overnight. Use a sharp knife to cut off the crusts and then place the bread (torn into pieces) into your food processor and process until very fine. You can also process bread that is not dried out and you'll get a nice breadcrumb topping. It won't be quite as crunchy, but still delicious. Store-bought are perfectly fine, too. We prefer plain Panko, for the best texture. 
The gratin can be prepared up to 24 hours in advance. Just don't add the breadcrumbs until just before baking. Keep the unbaked dish covered in the fridge and let it sit out for about an hour before baking. 
Leftovers will keep refrigerated for up to 5 days. Reheat in the oven or in the microwave until heated through. 

Nutrition

Calories: 336kcal | Carbohydrates: 18g | Protein: 11g | Fat: 25g | Saturated Fat: 15g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 7g | Trans Fat: 1g | Cholesterol: 74mg | Sodium: 206mg | Potassium: 302mg | Fiber: 2g | Sugar: 7g | Vitamin A: 2113IU | Vitamin C: 10mg | Calcium: 373mg | Iron: 2mg