Preparation

Make the crust

• Position a rack in the center of the oven and heat the oven to 350°F. Line a straight-sided 13×9-inch metal baking pan with a large piece of heavy-duty foil, leaving a 2-inch overhang on two sides.

  In a stand mixer fitted with the paddle attachment or in a large bowl with a hand mixer, beat the butter, sugar, orange zest, and salt on medium-high speed until light and fluffy, 1 to 3 minutes. Scrape the bowl. On low speed, mix in the flour until the dough is uniformly sandy, 1 to 2 minutes.

  Transfer the dough to the prepared pan and press evenly into the bottom. Bake until lightly golden, about 20 minutes. Let the crust cool completely on a wire rack.

  Melt the chocolate in a medium heatproof bowl set in a skillet of barely simmering water, stirring frequently, until smooth (be careful not to get any water in the chocolate). With a small offset spatula, spread all but about 2 Tbs. of the melted chocolate evenly over the cooled crust. Return the bowl with the remaining chocolate to the skillet of warm water and set aside off the heat to keep warm.

Make the topping

• Put 3 Tbs. of water in a heavy-duty 3-quart saucepan. Pour the sugar in the center of the pan and pat it down with a spatula just until evenly moistened. Cook over medium-high heat without stirring until the syrup turns amber, 6 to 8 minutes; swirl the pan as the sugar caramelizes to help it cook evenly. Slowly whisk in the cream (be careful—it will bubble vigorously and produce a lot of steam). Whisk in the butter and salt and boil until the butter is combined, 1 minute more.

Assemble the bars

• Pour the caramel evenly over the crust. Sprinkle the pine nuts over the caramel. Bake until the caramel is bubbling all over and jiggles only slightly in the center when the pan is nudged, 24 to 26 minutes. If necessary, reheat the remaining chocolate until fluid. With a spoon, drizzle the chocolate over the top. Let cool completely before cutting into squares.