Preheat the oven to 375°F (190°C). Place the tart pan on a parchment-lined baking sheet for easy transfer.
Lightly flour your work surface. Roll the thawed puff pastry just enough to smooth seams and slightly widen it. Press the pastry into a 9-inch tart pan, ensuring the bottom and sides are covered. Trim excess if needed.
Prick the bottom all over with a fork. Chill the pastry shell in the refrigerator for 15 minutes to help prevent shrinkage and keep it flaky.
Meanwhile, make the filling: in a large bowl, combine sliced apples and cranberries. Add sugar, cornstarch, orange juice, orange zest, cinnamon, nutmeg (if using), and salt. Toss until evenly coated. Let stand 5 minutes to get juicy.
Remove the chilled shell from the fridge. Arrange the fruit mixture in the tart shell, working in a spiral from the outside in for a neat look. Sprinkle the chopped nuts over the top and dot with small pieces of butter.
Brush exposed pastry edges with beaten egg. Sprinkle the top lightly with turbinado sugar.
Bake for 40–45 minutes, until the pastry is deeply golden and the apples are tender when pierced with a knife.
Cool in the pan for at least 20 minutes to help the filling set. Remove the tart ring, transfer to a rack, slice, and serve warm or at room temperature.