Salmon with Spinach & Feta Cheese Strudel

* Adapted From Epicurious.com

Ingredients:
1 10-ounce package frozen chopped spinach
1 medium onion, chopped
1/2 cup chopped leeks
1/2 cup unsalted butter
2 tablespoons all-purpose flour
1/3 cup milk
1/2 cup crumbled feta cheese
2 tablespoons freshly grated Parmesan
two 1/2 - 3/4-inch thick salmon fillets
six 18- by 14-inch sheets of phyllo, stacked between 2 sheets of wax paper and covered with a dampened kitchen towel

Instructions:
1. In a saucepan cook the spinach according to the package instructions, drain it, and let it cool. When the spinach is cool enough to handle, squeeze it dry by handfuls, transferring it as it is squeezed onto paper towel, to dry (the spinach should be very dry).
2. In the saucepan cook the onion and the leeks in 2 tablespoons of the butter over moderate heat, stirring, until they are softened. Stir in the flour, and cook the mixture, stirring, for 1 minute. Add the milk and and cook the mixture, stirring, for 3 minutes. (The mixture will be extremely thick.) Stir the onion-leek mixture into the spinach with the feta and salt and pepper to taste. The filling may be made 1 day in advance and kept covered and chilled.
3. Meanwhile, barbeque the salmon fillets, patted dry and seasoned with salt and pepper, for 5 to 6 minutes, or until it is just cooked through. Remove from the grill and let the salmon cool.
4. Preheat the oven to 425°F. In a small saucepan melt the remaining 5 tablespoons butter. On a work surface arrange two 20-inch-long sheets of wax paper with the long sides slightly overlapping and facing you. Put 1 sheet of the phyllo on the wax paper, brush it with some of the butter, and sprinkle it with about 2 teaspoons of the Parmesan on top. On this, layer, brush, and sprinkle 4 more sheets of the phyllo in the same manner and lay the sixth sheet on top.
5. Spread the spinach filling in a 3-inch-wide strip, mounding it on the phyllo 3 inches above the near long side, leaving a 2-inch border at each end, and arrange the salmon on top, pressing it gently into the filling. Using the wax paper as a guide, lift the bottom 4 inches of the pastry over the filling, fold in the ends, and roll up the strudel tightly. Transfer the strudel carefully, seam side down, to a lightly buttered baking sheet, brush it with the remaining butter, and bake it in the lower third of the oven for 25 minutes, or until it is golden.
6. Let the strudel cool to warm on the baking sheet on a rack. The strudel may be made 1 day in advance and kept covered loosely and chilled. Reheat the strudel in a preheated 400°F. oven for 15 minutes. Serve the strudel warm, cut into 1-inch slices with a serrated knife.