In the bowl of a food processor, combine eggs, salt, mayonnaise, sour cream, mustard, and pickle relish, pulsing until smooth. Cover, and refrigerate until cold, approximately 4 hours.
Preheat oven to 400°.
Line a rimmed baking sheet with parchment paper.
Place puff pastry cups 2 inches apart on prepared baking sheet.
Bake until golden brown, 10 to 15 minutes. Press center of cups down to create a cavity for the filling. Let cool completely.
Transfer egg mixture to a piping bag fitted with a medium open-star tip (Wilton #32). Pipe a decorative swirl into each puff pastry cup.
Garnish with chives, if desired. Serve immediately, or refrigerate, lightly covered, for up to 30 minutes before serving.
Recipe by TeaTime Magazine at https://teatimemagazine.com/egg-salad-in-puff-pastry-baskets/