Preparation

Make the shortbread crust:

• Line a straight-sided 13×9-inch metal baking pan with foil, letting the ends create an overhanging edge for easy removal. Lightly coat the sides of the foil (not the bottom) with nonstick cooking spray, oil, or melted butter to prevent the caramel from sticking.
• In a medium bowl, stir together the butter, brown sugar, and salt. Stir in the flour to make a stiff dough. Press the mixture evenly into the bottom of the prepared pan. Prick the dough all over with a fork. Refrigerate the pan for 30 minutes (or freeze for 5 to 7 minutes), until the dough is firm.
• Meanwhile, position a rack near the center of the oven and heat the oven to 325°F.
• Bake the dough for 20 minutes, and then decrease the oven temperature to 300°F and bake until the crust is golden all over and completely set, about 15 more minutes.

Make the topping:

•  Sprinkle the pecans evenly over the crust.
• In a heavy medium saucepan, bring the brown sugar, cream, butter, corn syrup, and salt to a boil over medium-high heat, stirring until all the ingredients are melted and smooth. Let the mixture continue to boil, without stirring, until a candy thermometer registers 240°F, about 6 more minutes. Turn off the heat and immediately (but carefully) pour the caramel evenly over the prepared crust. Let the bars cool completely, about 2 hours, before garnishing with the ganache.

Make the ganache:

• Put the chocolate in a small heat proof bowl. In a small saucepan, bring the heavy cream to a boil. Remove from the heat and pour over the chocolate. Let sit for 3 minutes. Stir gently with a rubber spatula until combined and smooth.
• Fill a plastic zip-top baggie with the ganache, snip the tip off a corner, and drizzle the ganache decoratively over the caramel bars (you don’t have to use all the ganache; keep the extra in the fridge for 5 days). Let the ganache set for 30 minutes to an hour. Carefully lift the bars from the pan using the foil sides and transfer them to a cutting board. Separate the foil from the bars by sliding a spatula between them. Cut the bars into 1-1/2-inch squares. They will keep at room temperature for 1 week.