- 1 sheet frozen puff pastry (half of a 17.3-ounce package), thawed
- 1 1/2 pounds cod, haddock or other flaky white fish fillets
- 1 1/2 pounds salmon fillet, skin removed
- 2 (10 ounce) boxes frozen spinach, thawed, squeezed dry, 1 1/2 cups spinach liquid reserved (do this in sieve or colander set over large bowl)
- 1/3 cup butter
- 2 medium-large onions, cut into medium dice
- 9 tablespoons all-purpose flour
- 1 (12 fluid ounce) can evaporated milk, microwaved until very hot
- 3/4 cup Parmesan cheese
- 1/2 teaspoon salt and ground black pepper
- 2 ounces smoked salmon, cut into small dice
- Adjust oven rack to lower-middle position and heat oven to 400 degrees. Cut puff pastry sheet into 4 squares and then each square into 2 triangles. Place triangles on a parchment-lined cookie sheet; prick all over with a fork. Bake until puffed and golden, about 15 minutes. Remove from oven; set aside.
- Meanwhile, bring cod, salmon and spinach liquid to simmer over medium heat in a covered deep skillet. Continue to simmer over low heat until fish is opaque, 4 to 5 minutes. Transfer fish with a slotted spoon to a medium bowl and break into large chunks, pouring off excess liquid; set aside. Strain and reserve 2 cups of the fish cooking liquid.
- Return skillet to burner; add butter and melt over medium-high heat. Add onions; saute until tender, 4 to 5 minutes. Whisk in flour, then hot milk and reserved cooking liquid; cook until sauce boils to thick sauce consistency, 1 to 2 minutes. Whisk in cheese and season to taste with salt and pepper. Stir sauce, along with spinach and smoked salmon into fish. Pour mixture into a 13-by 9-inch Pyrex baking dish. Cover with foil and bake until bubbly about 10 minutes. Spoon a portion of filling onto each plate, top with a pastry triangle, and serve.