¼ cup honey
¼ cup sugar
½ tsp. kosher salt
2 Tbsp. unsalted butter
1 Tbsp. apple cider vinegar
1 lb. apricots (about 6), halved lengthwise, pits removed
1 sheet frozen puff pastry (one 14-oz. package or half of a 17.3-oz. package), thawed
¼ cup raw pistachios, finely chopped
Whipped cream or vanilla ice cream (for serving; optional)
Place a rack in middle of oven and preheat to 425°. Cook honey, sugar, salt, and 2 Tbsp. water in a small saucepan over medium-high heat, stirring occasionally, until caramel turns dark amber in color (because of the honey, it can be hard to tell when the color changes; it should look like maple syrup). Remove caramel from heat and add butter and vinegar (be careful; mixture will bubble up). Stir with a wooden spoon or heatproof rubber spatula to incorporate.
Pour caramel into a 9"- or 10"-diameter cake, tart, or springform pan or skillet and swirl to evenly coat the bottom.
Arrange apricots, cut side down, in pan, letting them overlap slightly if needed. (Depending on the pan you use, you may not need all of them.)
Unfold pastry and gently roll out on a lightly floured surface just to soften the creases and corners. Prick pastry all over with a fork. Drape over pan, then, using kitchen shears, trim to make a circle that’s slightly larger than the circumference of the pan (remember, the dough will shrink as it bakes) and tuck into pan.
Bake tart until pastry is puffed and just golden, 15–20 minutes. Reduce oven temperature to 375° and continue to bake until pastry is deep golden brown and fruit juices are bubbling, 15–20 minutes longer. Transfer tart to a wire rack and let cool 10 minutes.
Invert a large plate over the top of the pan. Using a dish towel or oven mitts, flip tart over onto plate. Carefully remove pan. Top tart with pistachios.
Serve tart with whipped cream or ice cream if desired.
Do Ahead: Tart can be baked 4 hours ahead. Leave in pan at room temperature. If caramel has set too firmly to release from pan, heat in a 375° oven 5 minutes to warm and loosen before turning out.
Recipe adapted from Bon Appetit magazine.