Tuna and Mushroom Melt Turnovers

Directions

1. Saute the onion in the butter for 2 minutes. Add the mushrooms and saute until tender, about 12 to 15 minutes. Set aside and cool to room temperature.
2. Flake tuna into a medium sized bowl. Stir in the mushroom mixture, egg yolk, cheese, salt and pepper. Blend well. Refrigerate until cold.
3. Thaw frozen pastry sheets 20 minutes at room temperature. You want them pliable but still cold. Roll out each sheet on a lightly floured surface to a 13-inch square, cut into 4 equal quarters. Repeat with a second sheet.
4. Divde the filling equally between the 8 pastry squares, leave a 1 inch border of uncovered pastry on all sides. Brush the borders with some of the beaten egg white. Fold the squares diagonally in half to form triangles. Press the edges firmly together. Brush the tops with the egg white. Pierce the top of each turnover in the center with a small paring knife to allow the steam to escape.
5. Arrange the turnovers on a cookie sheet 1 inch apart. Place in the freezer while the oven heats to 450 degrees F.
6. Place in the oven and immediately lower the temperature to 400 degrees F.  Bake for 20 minutes.
7. In the meantime, combine in a medium sauce pan the ingredients for the Mushroom Cheese Sauce. Simmer on medium low until the cheese melts and sauce is smooth.
8. Serve the turnovers with the sauce spooned over the top.