Preheat the oven to 425 degrees F.
Roll out one pie dough disc into a 12-inch circle, and fit it into a 9 inch pie pan, without stretching the dough. Trim the edges.
In a large bowl, toss together the apple slices, cranberries, sugar, corn starch, cinnamon, nutmeg and salt, until evenly coated. Pour the apples into the pie pan and spread them around evenly.
Roll out the second disc and place it over the apples (or cut into strips for a lattice crust). Roll and crimp the edges of the dough together to make a tight seal.
For an extra golden and crunchy top crust, brush with a beaten egg yolk and sprinkle with coarse sugar.
Bake for 20 minutes in the preheated oven, laying a sheet of aluminum foil over the top if it starts to brown too quickly. Lower the temperature to 375 degrees F and bake for another 40-45 minutes, until the juices are bubbling and the crust is golden brown.
Let cool for an hour before serving.