Prepare Filling: Preheat oven to 350°. Melt 1/3 cup butter in a large saucepan over medium heat; add all-purpose flour, and cook, whisking constantly, 1 minute. Gradually add chicken broth and milk, and cook, whisking constantly, 6 to 7 minutes or until thickened and bubbly. Remove from heat, and stir in Creole seasoning.

Melt 2 Tbsp. butter in a large Dutch oven over medium-high heat; add onion and mushrooms, and sauté 10 minutes or until tender. Stir in chicken, next 4 ingredients, and sauce.

Prepare Crust: Place 1 piecrust in a lightly greased 10-inch cast-iron skillet. Spoon chicken mixture over piecrust, and top with remaining piecrust.

Whisk egg white until foamy; brush top of piecrust with egg white. Cut 4 to 5 slits in top of pie for steam to escape.
Bake at 350° for 1 hour to 1 hour and 5 minutes or until golden brown and bubbly.

Because Joe and I like a lot of gravy a doubled the sauce.