In a small bowl, combine the scallops (or shrimp), cream, onions, parsley, dill, garlic, pesto, salt & pepper. In another small bowl, beat egg white on medium speed until soft peaks form; fold into scallop mixture.
Assembly
Preheat oven to 400 F. Line a 15 x 10 x 1-inch baking sheet with parchment paper.
On a lightly floured surface, roll each pastry sheet into a 12 x 10-inch rectangle. Cut each sheet into FOUR- 6 x 5-inch rectangles. Divide mushroom mixture evenly & spread over 4 pieces of pastry leaving a 1/2-inch border.
Center the salmon pieces on top. Next, top each salmon piece with a quarter of the scallop filling.
Top each with a pastry rectangle & crimp to seal. With a sharp knife, cut several slits in the top to let steam escape. Place on the baking sheet & brush with egg wash. Bake for 20-25 minutes or until a thermometer reads 160 F.
Dill Cream Sauce
While salmon is baking, mix all sauce ingredients & refrigerate until serving time.