In a bowl, combine salmon, scallops (or shrimp), cream, onions, parsley, dill, garlic, pesto, salt & pepper. In another bowl, beat egg white on medium speed until soft peaks form; fold into seafood mixture. Set aside in refrigerator.
Cut 2 pieces of parchment paper to fit a baking sheet at least 12 X 12-inch in size. Remove 1 sheet of thawed, puff pastry from refrigerator & roll out on 1 of the sheets of parchment to form an 11 1/2-inch square. Using a pot lid or bowl, cut the largest possible circle from the pastry. Transfer the pastry (on parchment) to baking sheet & place in refrigerator. Repeat procedure with the second piece of pastry.
Remove the first pastry circle from the fridge. Spread the filling mixture on the circle, to within 1/4-1/2-inch of the outer edge. Use a pastry brush to lightly wet the edge of the pastry. Top with the second circle of pastry, using your fingers to lightly press the pastry together.
Place a 2 1/2-inch diameter glass or jar lid in the center of the pastry. Use a ruler & the tip of a sharp paring knife to score the pastry from the edge of the glass to the outer edge of the pastry at 12, 3, 6 & 9 o’clock. Score each quarter in half, making 2 triangles. You will have 8 triangles when your’e done. Place tart in freezer for NO MORE than 5 minutes before continuing.
Use a sharp scissors to cut each triangle cleanly along the score lines from the outer edge of the glass. Remove the glass. Place your index finger of your left hand at the top of a triangle (where the glass was). Use your right hand to twist that triangle 3 times. Go around the circle, repeating with each of the remaining triangles. Refrigerate tarte for at least another 5 minutes.
Preheat oven to 400 F. Prepare egg wash & brush it over the tarte. Bake about 20 minutes. Rotate the tarte 180 degrees & lower the temperature to 375 F. Bake another 10 minutes or until a rich golden brown color. Remove from oven & transfer to serving dish. Nice to serve with a dill cream sauce & fresh steamed broccoli florets.