Peel, core, and slice the apples into 2-inch (5cm) slices.
In a large bowl, combine the apples, butter, sugar, cornstarch, cinnamon, and salt.
Using parchment paper, make two “straps” and set them in the bottom of the Dutch oven to create a handle to pull out the pie once cooked.
Roll out one of the pie crusts about 2 inches (5cm) larger than the Dutch oven. Place the pie crust in the bottom of the Dutch oven. Cut the remaining pie crust into 1-inch (2 1/2cm) strips and set aside.
Pile the apple slices in the Dutch oven.
Create a lattice top over the apple slices with the reserved pie crust strips. Combine the beaten egg with 1 tablespoon of water. Brush the egg mixture over the lattice top.
Cover the Dutch oven with the lid and set over 14 hot coals. Place 10 to 12 coals on top. The coals may need to be replaced halfway through cooking to maintain a 350 degrees F (175 degrees C) temperature. Cook until the crust is golden brown and the filling is bubbly. This takes about 1 hour.