01 - Set oven to 400°F (200°C) to preheat while preparing ingredients.
02 - In a 9-inch ovenproof skillet or tarte Tatin pan, melt 1/2 cup sugar over medium heat without stirring until deep amber in color. Gently swirl the pan for even coloring.
03 - Stir in unsalted butter, vanilla extract, salt, and ground cinnamon (if using) until caramel mixture is smooth.
04 - Position apple quarters cut side up in the caramel, packing tightly. Simmer over medium heat for 12 to 15 minutes, occasionally basting with caramel, until apples are slightly softened and caramel thickens. Remove from heat.
05 - Roll out puff pastry to a size just larger than the skillet. Carefully drape it over cooked apples and tuck the edges down along the sides.
06 - Transfer pan to preheated oven and bake for 25 to 30 minutes, until pastry is golden brown and crisp.
07 - While tart bakes, line a baking sheet with parchment. In a small saucepan, combine 1/3 cup sugar with 1 tablespoon water. Cook over medium heat without stirring until golden amber. Stir in sea salt and crushed hard candies, immediately pour onto prepared sheet, and cool completely. Once set, break into small shards.
08 - Cool baked tart for 5 minutes. While still warm, invert onto a serving plate.
09 - Right before serving, scatter candy crunch shards over the tart for added sweetness and texture.