- 6 Gala apples (preferably red; 2 3/4 pounds)
- 1/2 cup water
- 1/2 cup sugar
- 1/2 vanilla bean, split lengthwise
- 1 (17 1/4-oz) package frozen puff pastry sheets, thawed
- All-purpose flour for dusting
- 1 1/2 tablespoons unsalted butter, melted
- Special equipment: parchment paper
- Accompaniment: vanilla ice cream
- Put oven racks in upper and lower thirds of oven and preheat oven to 400°F. Line 2 large baking sheets with parchment paper.
- Peel apples, reserving skins. Stir together water and 6 tablespoons sugar in a 1-quart heavy saucepan, then scrape in seeds from vanilla bean and add pod. Add reserved apple skins and bring to a boil, stirring until sugar is dissolved. Remove from heat and let stand 10 minutes. Pour through a medium-mesh sieve into a bowl, pressing hard on and then discarding solids.
- Roll out 1 pastry sheet into a 10-inch square on a lightly floured surface with a lightly floured rolling pin, then cut in half and transfer to 1 of baking sheets. Repeat with remaining pastry sheet, transferring to second baking sheet.
- Halve apples lengthwise, then core with a melon-ball cutter or a small spoon and cut crosswise into very thin slices (1/8 inch thick or less), keeping apple halves intact. Fan apple slices slightly, keeping apple shape, then arrange 3 halves in a row on each piece of pastry, leaving a 2/3-inch border on all sides.
- Brush border lightly with syrup and fold over about 1/3 inch to touch edges of apples. Crimp edges with a fork, then brush apples and edges of pastry with syrup (reserve remaining syrup). Brush apples completely with melted butter, then sprinkle evenly with remaining 2 tablespoons sugar.
- Bake tarts in upper and lower thirds of oven 20 minutes, then switch position of sheets and reduce oven temperature to 375°F. Bake tarts until edges are golden, 15 to 20 minutes more. (If pastry edges aren't browning evenly, rotate tarts 180 degrees on sheets halfway through baking.)
- While tarts bake, boil remaining syrup over moderate heat until reduced to about 1/4 cup, 30 seconds to 1 minute.
- Let tarts stand 5 minutes, then brush warm apples with remaining syrup.