-
If pastry comes as 1 sheet, cut crosswise in half. Roll out each piece of pastry into a 13-inch square on a lightly floured surface with a lightly floured rolling pin. Chill on baking sheets until firm, about 1 hour.
-
Cut out 3 rounds from each sheet of puff pastry using template. Brush any excess flour from both sides of pastry rounds. Brush tops with some of beaten egg. Chill pastry rounds on baking sheets until firm, about 1 hour.
-
Preheat oven to 425°F with rack in middle.
-
Divide cold soup among bowls. (Do not chill soup in bowls.) Lightly beat yolk, then brush around edge and down side of each bowl (a 1/2-inch-wide strip). Working quickly, place each pastry round over a bowl and pull slightly so pastry is taut. Press edge down against side of bowl to seal tightly.
-
When all bowls are covered with pastry, arrange in a large 4-sided sheet pan and bake until pastry is puffed and golden brown, 15 to 20 minutes. Serve immediately.