For the crust
1 box (2 sheets) puff pastry, thawed
1 egg, lightly beaten

For the filling
2 baking apples, peeled and cored (I've used both Honeycrisp and Gala)
3 tablespoons unsalted butter, divided
1/2 cup packed dark brown sugar
1 tablespoon all-purpose flour
2 teaspoons freshly squeezed lemon juice
1/2 teaspoon ground cinnamon
Pinch of kosher salt

For the icing
4 ounces cream cheese
1 cup powdered sugar
1 teaspoon pure vanilla extract