Preheat the oven to 450 F - mark 8. Lightly brush a baking sheet with the softened butter. Sprinkle with water; set aside.
Prepare the pastry cases: dust a work surface with flour. Roll out the puff pastry about 1/8 inch thick and cut into 6 rectangles, 4 inches long x 2.5 inches wide. Or, use an oval cutter of approximately the same dimensions, if available.
Transfer the shapes to the baking sheet with a palette knife. Brush the tops with egg glaze. Be careful not to let the egg drip over the edges of the pastry, or it will not rise evenly. Refrigerate for 10 minutes.
When chilled, brush again with egg glaze and bake for about 25 minutes, until puffed and golden.