Preheat your oven to 375°F (190°C).
Prepare the apples by peeling, coring, and slicing them into thin pieces.
In a large bowl, toss the sliced apples with sugar, lemon juice, cinnamon, nutmeg, and cornstarch.
Roll out the pie pastry and fit it into a greased baking sheet or slab pie dish.
Fill the pastry with the apple mixture, spreading it evenly across the crust.
Roll out a second piece of pastry and place it over the filling, pinching the edges to seal.
Brush the top crust with the beaten egg mixed with milk for color.
Bake in the preheated oven for 45-50 minutes until the crust is golden brown.
Allow the pie to cool for at least 30 minutes before slicing.
Serve warm or at room temperature, optionally with ice cream or whipped cream.