When I lived in Seattle, one of my favorite places was a small stand that sold piroshki—Russian stuffed pocket sandwiches. Whenever I’m missing my former town, I make my own batch.
In a large skillet, cook the beef, onion, garlic, salt and pepper over medium heat until meat is no longer pink; crumble beef; drain. Cool to room temperature.
Stir the spinach, cheese, sour cream and dill into the beef mixture. On a lightly floured surface, roll a puff-pastry sheet into a 12-in. square. Cut into sixteen 3-in. squares. Repeat with remaining sheet.
Spoon 1 tablespoon beef mixture onto the center of each square. Fold dough over filling, forming a triangle; press edges with a fork to seal. Transfer to greased baking sheets. Whisk egg and water; brush over tops. Bake at 400° until golden brown, 14-16 minutes.