Preheat oven to 400°F (200°C). Line a baking sheet with parchment.

Toss apples, cranberries, sugars, lemon juice, cinnamon, and cornstarch in a bowl until coated.

Roll crust into a rough 11-inch circle on the baking sheet. Pile fruit in the center, leaving a 2-inch border.

Fold the edge over the fruit in pleats, pressing gently to seal. Brush crust with beaten egg and sprinkle coarse sugar.

Bake 30–35 minutes until crust is golden and filling bubbles. Cool 10 minutes before slicing.