How to Make It
Preheat the oven to 450°. On a lightly floured sheet of parchment paper, roll out the Flaky Tart Pastry to a 13-inch round. Transfer the pastry and parchment to a baking sheet.
Spread the onion slices on the tart in a single layer, leaving a 1-inch border. Season with salt and pepper. Fold the edge of the pastry over onto the onion and brush the rim with the egg wash. Bake for about 20 minutes, or until the pastry is golden. Let cool.
Arrange the salmon on the tart. With a warm fork, stir the crème fraîche and drizzle it over the tart. Sprinkle the parsley, dill and lemon juice on top and serve.