1½ sticks cold unsalted butter, chilled and cut into cubes
¼ cup ice water
1 tablespoon distilled white vinegar
1½ sticks unsalted butter
1¼ cups light brown sugar
½ cup honey
½ teaspoon salt
¼ teaspoon curry powder (optional)
1 cup heavy cream
1 pound pecan halves
Crust: In a food processor, pulse the flour with the sugar and salt, then add the butter and process until the mixture resembles coarse meal. Sprinkle the water and vinegar, process until the crumbs are evenly moistened. Turn the crumbs out onto a sheet of wax paper and knead just until the dough comes together. Pat the dough into a disk, wrap in plastic and refrigerate until slightly chilled, about 15 minutes.
Preheat the oven to 375 and line the bottom of a 9-by-13-inch baking pan with parchment paper (to help lift out later). Roll out the dough between 2 sheets of wax paper to fit in the bottom of the pan (about ⅓ inch thick). Place it in the baking pan and refrigerate the dough until firm, about 30 minutes.
Line the dough with parchment paper and fill with pie weights or dried beans. Bake for about 20 minutes, until the dough is just set. Remove the parchment paper and weights and bake the crust for about 12 minutes longer, until lightly golden and set. Let cool.
Topping: In a large saucepan, combine the butter, brown sugar, honey and salt and cook over moderate heat, stirring, until foamy and slightly thickened, about 10 minutes. Add the curry powder (optional) and cream and cook, stirring occasionally, until a candy thermometer inserted in the caramel registers 240 (soft ball stage), about 10 minutes longer. Add the pecans and cook for 2 minutes more and pour the filling over the crust, spreading it evenly. Bake for about 15 minutes, until the crust is golden and the topping is bubbling. Let cool completely. Slide the parchment onto a cutting board. Cut into the bars and serve.
* The bars can be stored in an airtight container at room temperature for up to 1 week.