Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper.
On the parchment paper, roll out your pie crust into a 12-inch circle.
In a mixing bowl, toss apple and pear slices with lemon juice, sugar, cinnamon, and nutmeg until evenly coated.
Arrange the fruit in the center of the crust, leaving about a 2-inch border all around.
Fold the edges of the crust up and over the fruit, pleating as you go to seal in the filling.
Dot the fruit with cubed butter.
Beat the egg and brush it over the folded crust edges, then sprinkle the crust with coarse sugar.
Bake for 30–35 minutes, or until the crust is golden and the fruit is tender and bubbly.
Let cool for 10–15 minutes before slicing and serving.