Directions

1. Preheat oven to 350°F, and place a baking sheet on the lowest rack to catch any drips from the pie. Toss apples, rhubarb with cinnamon, flour and ¾ cup granulated sugar.
2. Melt butter in a 10-inch cast-iron skillet over medium heat; add brown sugar, and cook, stirring constantly, 1 to 2 minutes or until sugar is dissolved. Remove from heat and allow to cool slightly.
3. Place 1 pie crust in skillet over brown sugar mixture. Spoon fruit mixture over pie crust, and top with remaining pie crust. Whisk egg white until foamy. Brush top of piecrust with egg white; sprinkle with 2 tablespoons granulated sugar. Cut 4 or 5 slits in top for steam to escape.
4. Bake at 350F for 1 hour to 1 hour and 10 minutes or until golden brown and bubbly, shielding with aluminum foil during last 10 minutes to prevent excessive browning, if necessary.
5. Cool on a wire rack 30 minutes before serving.