Special equipment: A 1 1/2-inch and a 3/4-inch round cookie cutter or the round end of a pastry tip A pastry bag or resealable plastic bag
Position an oven rack in the center of the oven, and preheat to 400 degrees F. Line a rimmed baking sheet with parchment.
Unfold the pastry, and cut out rounds with a 1 1/2-inch round cookie cutter (you should get roughly 40). Space them at least 1 inch apart on the prepared baking sheet. Lightly score the center of each round with a 3/4-inch cookie cutter (don't press all the way through). Lightly brush each round with the egg.
Invert another rimmed baking sheet on top of the dough rounds, and bake for 5 minutes. (Covering the rounds helps them puff straight up evenly.) Remove the top baking sheet, and continue to bake until golden, 8 to 10 minutes more. Let the rounds cool completely on the baking sheet, then use the handle of a wooden spoon to gently punch a hole in the middle of each round. (The baked pastry can be stored at room temperature in an airtight container for up to 1 day or frozen for up to 1 month.)
Meanwhile, microwave the vinegar and sun-dried tomatoes in a small bowl, covered, for 30 seconds; let cool. Reserve 1 teaspoon of the vinegar, and finely chop the tomatoes. Finely shred the cucumber, and squeeze out all the excess moisture. Mash together the tomatoes, reserved vinegar, shredded cucumber, cream cheese, chives and 1/4 teaspoon salt with a fork in a medium bowl until smooth. Transfer the cream cheese filling to a pastry bag or resealable plastic bag (cut off the tip). (The filling can be refrigerated for up to 1 day.)
Tear or cut the salmon into 40 small pieces, and roll each into a rough rosette shape. Pipe some of the filling into each puff. Top each with a piece of salmon, and sprinkle with sesame seeds. (The salmon puffs can be refrigerated for up to 2 hours.)
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