Preheat oven to 425°F. Roll out each pastry sheet on lightly floured surface to 12-inch square. Cut each in half, forming four 12×6-inch rectangles.
Place 1 salmon fillet in center of each rectangle, about 3 inches in from and parallel to 1 short edge. Sprinkle each fillet with salt, pepper,
Heat a medium size fry pan on medium high, add the shallots and stir to cook, add the shrimp and cook until pink, add tarragon, spinach, lemon juice, then deglaze with white wine. Then add brie and mix until well blended.
Top each salmon fillet with 3 shrimp and some of the spinach-brie mixture.
Brush edges of pastry with some beaten egg.
Fold long sides of pastry over fillets. Fold short edge of pastry over fillets and roll up pastry, enclosing fillets. Seal edges of pastry. Place pastries, seam side down, on baking sheet.
Cut a couple of vents on each pastry then brush with beaten egg.
Bake pastries until dough is golden brown, about 20 minutes. Remove from oven; let stand 10 minutes.