Preheat oven to 400°F (200°C). Line a large baking sheet with parchment paper.
Unfold the cold puff pastry onto the prepared baking sheet. Gently roll into an approximately 10 x 12-inch (25 x 30-cm) rectangle, smoothing the fold lines as you roll.
1 sheet (245 g) frozen puff pastry
Using a sharp knife, lightly score a ¾-inch (2-cm) border around the pastry without cutting all the way through. Prick the center of the pastry several times with a fork, leaving the border untouched so it can rise during baking.
Core the apples and slice them evenly, about ⅛-inch (3-mm) thick. Leave the peels on to add color to the finished tart.
1 medium Granny Smith apple, 1 medium Dazzle apple
Place the sliced apples in a medium bowl. Add the cinnamon, salt and lemon juice and toss carefully until evenly coated.
½ tsp (1.3 g) ground cinnamon, ⅛ tsp (0.8 g) table salt, 1 tsp (5 ml) fresh lemon juice
Arrange the apple slices in slightly overlapping rows inside the scored border, alternating the Granny Smith and Dazzle slices. Keep the apples in a single layer with some overlap so they become tender during the short baking time and the pastry underneath can bake properly.
Stir together the melted butter and brown sugar in a small bowl until evenly mixed. Brush or spoon the brown sugar butter mixture over the apples.
2 tbsps (28 g) unsalted butter, 2 tbsps (25 g) packed light brown sugar
Whisk together the egg and water. Brush the egg wash over the exposed puff pastry border, then sprinkle with coarse sugar. The coarse sugar is completely optional, but is used to sweeten the pastry if you want to.
1 large egg, 1 tsp (5 mL) water, 1 tbsp (12 g) coarse sugar
Bake for 22–26 minutes, until the pastry border is puffed and golden and the apples are tender and lightly caramelized. Use the color of the pastry as a doneness cue rather than removing the tart while the pastry is still pale.
Cool on the baking sheet for 5–10 minutes before slicing and serving. Serve with vanilla ice cream if you want.
vanilla ice cream