Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper to prevent sticking and make cleanup easier.
Core the apples and slice them thinly, about 1/8 inch thick. You can peel them or leave the skins on for extra color and texture. Place the apple slices in a medium bowl.
2-3 medium apples
Add the granulated sugar, brown sugar (if using), cinnamon, nutmeg, and a pinch of fine sea salt to the apples. Toss gently until the slices are evenly coated. Let sit for about 5 minutes so the apples release a little juice and soften slightly.
2-3 medium apples, 2 tablespoons granulated sugar, 1 tablespoon light brown sugar, 1 teaspoon ground cinnamon, 1/8 teaspoon ground nutmeg, 1 pinch fine sea salt
On a lightly floured surface, roll the puff pastry sheet into roughly a 10×12-inch rectangle. It doesn’t need to be perfect. Transfer the rolled pastry to the prepared baking sheet.
1 sheet frozen puff pastry
Using the tip of a sharp knife, lightly score a 1/2-inch border all the way around the edge of the puff pastry, like a picture frame, without cutting all the way through. This will form the raised crust.
1 sheet frozen puff pastry
Prick the pastry all over inside the scored border with a fork. This helps keep the center from puffing too much so the apples can sit nicely on top.
1 sheet frozen puff pastry
Lay the seasoned apple slices inside the border in overlapping rows, in straight lines, diagonals, or a spiral pattern. Aim for a fairly even single layer; a bit of overlap is fine, but avoid piling the apples too high so they bake evenly.
2-3 medium apples
Brush the apples lightly with the melted butter. Then brush the outer border of the puff pastry with the beaten egg wash (or milk), which will help it bake up golden and glossy.
1 tablespoon unsalted butter, 1 large egg
Bake the tart for 20–25 minutes, or until the pastry is puffed and deeply golden and the apples are tender. If the edges start to brown too quickly, tent them loosely with foil for the last few minutes of baking.
While the tart bakes, gently warm the apricot jam or apple jelly in a small saucepan or microwave-safe bowl until fluid. Stir in 1–2 teaspoons of water as needed until it reaches a maple-syrup-like consistency.
3 tablespoons apricot jam or apple jelly, 1-2 teaspoons water
Remove the tart from the oven and immediately brush the warm glaze over the apples to add shine and flavor. Let the tart cool for at least 10–15 minutes to allow the juices to settle and keep the pastry crisp.
3 tablespoons apricot jam or apple jelly, 1-2 teaspoons water
Cut the tart into 6–8 squares or strips. Dust with powdered sugar if desired, and serve warm or at room temperature with vanilla ice cream or whipped cream.
powdered sugar, vanilla ice cream or whipped cream