How to Make It
Preheat oven to 325°F. On a lightly floured work surface, roll pastry sheet to a 15- x 10-inch rectangle (about 1/4 inch thick). Place on a parchment paper–lined baking sheet. Sprinkle with 3 tablespoons sugar. Shingle apple and mango slices in alternating crosswise rows, leaving a 1-inch border. Sprinkle with 1 tablespoon sugar and 6 tablespoons butter pieces.
Bake tart in preheated oven until puff pastry is golden brown, about 40 minutes. Remove tart from oven, and top with a second sheet of parchment and a second baking sheet. Carefully flip so tart lands fruit side down on second baking sheet. Remove first baking sheet, and peel parchment from pastry. Sprinkle pastry with remaining 2 tablespoons sugar and remaining 2 tablespoons butter pieces. Return tart to oven; bake at 325°F until pastry is very crispy, about 40 minutes. Let cool 15 minutes. Carefully invert tart onto original baking sheet or a serving platter; remove and discard parchment.
Heat sugar in a medium saucepan over medium until it melts and turns golden brown, about 5 minutes, stirring during last 2 minutes. Carefully whisk in cream and butter. Remove from heat; let cool.
Cut tart into 3- x 5-inch pieces. Serve with caramel sauce and ice cream. Garnish with basil and lemon zest.