For the Crust
In a food processor, pulse the flour with the sugar and salt. Add the cubed butter and process until the mixture resembles coarse meal. Sprinkle on the ice water and vinegar and 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°. Line the bottom of a 9-by-13-inch metal baking pan with parchment paper. Roll out the dough between 2 sheets of wax paper to an 11- by-15-inch rectangle (1/4 inch thick). Trim the dough to a 9-by-13-inch rectangle and place it in the baking pan. Cut the remaining dough into 3/4-inch-wide strips and press them up the side of the pan to form a rim all around. 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 25 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.

For the 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 (if using) 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 longer. 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 bars and serve.