Step 1: For the Shortbread Crust: In a large bowl, whisk together the all-purpose flour, granulated sugar, and salt.
Step 2: Add the cold, cubed unsalted butter. Using your fingertips or a pastry blender, cut the butter into the dry ingredients until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
Step 3: Slowly add the ice-cold water, one tablespoon at a time, mixing gently until the dough just comes together. It should be shaggy but hold together when pressed.
Step 4: Form the dough into a disc, wrap it tightly in plastic wrap, and refrigerate for at least 30 minutes.
Step 5: Preheat your oven to 375°F (190°C). On a lightly floured surface, roll out the chilled dough into a 12-inch circle. Carefully transfer it to a 9-inch tart pan with a removable bottom. Press the dough gently into the bottom and up the sides of the pan. Trim any excess dough.
Step 6: Prick the bottom of the crust all over with a fork. Line the crust with parchment paper and fill with pie weights or dried beans. Blind bake for 15 minutes.
Step 7: Remove the parchment and weights, then continue baking for another 8-10 minutes, or until the crust is lightly golden brown. Let cool completely on a wire rack.
Step 8: For the Smoked Maple Miso Caramel Filling: In a heavy-bottomed saucepan over medium heat, combine the granulated sugar and water. Stir gently until the sugar dissolves.
Step 9: Bring the mixture to a boil without stirring. Cook until it reaches a deep amber color, gently swirling the pan if needed to ensure even caramelization (8-12 minutes).
Step 10: Carefully and slowly pour in the warm heavy cream while whisking continuously. The mixture will bubble up vigorously, so be cautious. Continue whisking until smooth.
Step 11: Remove from heat and stir in the cubed butter, smoked maple syrup, white miso paste, vanilla extract, and a pinch of flaky sea salt. Whisk until all ingredients are fully incorporated and the caramel is smooth and glossy.
Step 12: Immediately pour the warm caramel into the cooled, pre-baked tart crust. Spread evenly.
Step 13: For the Toasted Pecan Topping & Assembly: While the caramel is still warm and slightly tacky, arrange the toasted pecan halves decoratively over the surface of the caramel.
Step 14: Refrigerate the tart for at least 4 hours, or preferably overnight, until the caramel is completely set.
Step 15: Once set, carefully remove the tart from the pan. Allow it to sit at room temperature for 15-20 minutes before slicing and serving. Garnish with an additional sprinkle of flaky sea salt if desired.