Onion gratin

This a terrific side dish, especially for Thanksgiving. I've been making this recipe since November 2009. It's always a hit. One word of caution: the red onions can turn gray. I enjoy the flavor of red onions and the color doesn't bother me, but see the Variations if this dish needs to be perfect. The inspiration for this dish came from a Gourmet Magazine recipe.

  
    Recipe serves
    Active time
    Total time
  

    8 people
    40m
    1h
  

  
    Special equipment needed
  
    1 or 2 large skillets
  
    2 quart shallow gratin baking dish

  
    Ingredients
  
tablespoons butter, cut into 7 pieces, divided usage
  
tablespoons all-purpose flour
  
cups milk
  
teaspoon salt
  
    1/2 teaspoon pepper
  
leeks, carefully cleaned and chopped
  
red onion, chopped
  
large yellow onion, sliced
  
garlic cloves, chopped
  
14-ounce bag frozen pearl onions, thawed
  
cup fresh breadcrumbs
  
    1/4 cup chopped parsley

  
    Special note
  
    • Leeks can contain a lot of dirt. Cut the leek lenghtwise and examine it. Separate the layers and carefully rinse away all dirt. See picture below.

  
    Variations
  
    • Use 1/2 pound of shallots instead of the red onion for a slightly prettier gratin. A yellow or white onion can also be substituted.

  
    Storage
  
    • This dish can be cooked several hours ahead. Cover loosely and leave at room temperature. Add the breadcrumb mixture just before cooking.
  
    • Store any uneaten gratin covered in the refrigerator for 3 - 4 days.

Instructions
• Butter the gratin pan thoroughly.
• Melt 4 tablespoons of butter in a large skillet over medium heat. Add the flour and whisk. Cook for 2-3 minutes without letting it burn. This is called a roux.
• Gradually add the milk or stock to the roux, whisking constantly to remove any lumps. In about 5 minutes, the sauce should thicken. This is your Béchamel sauce. Add the salt and pepper. Stir to combine. Set aside until the onions are cooked.
• If necessary, put the sauce in a bowl and wash the skillet.
• Add the remaining 3 tablespoons of butter to the skillet. When the butter is melted, add the leeks and onions. Sauté over medium heat until they are softened, about 20 minutes. Add the garlic and cook 1 minute.
• Preheat oven to 425º.
• Add the pearl onions and cook until tender, about 10 minutes.
• Add the Béchamel sauce and combine thoroughly. Put the mixture into the prepared gratin pan.
• Just before putting the gratin in the oven, combine the breadcrumbs and parsley. Bake for 20 minutes until hot and golden on top.

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