Turtle Bars

Preheat the oven to 350°F (175°C) . Position a rack in the lower third of the oven. Line a 13 x 9 x 2-inch pan over the bottom and sides with heavy-duty aluminum foil. To make the crust: cut the butter into chunks and melt it in a large saucepan over medium heat. Remove from the heat and stir in the sugar, vanilla, and salt. Add the flour and mix just until incorporated. Press the dough evenly over the bottom of the pan. Scatter the pecans over the dough. Bake until the pecans are lightly toasted, 10 to 12 minutes. Set the pan aside but leave the oven on while making the topping. To make the topping: combine the butter and brown sugar in a small saucepan. Bring the mixture to a boil over medium heat, stirring occasionally. Boil for 1 minute (mixture may look curdled). Pour the hot butter mixture over the pecans on the crust. Bake for 15 to 18 minutes, or until the topping is dark and bubbling vigorously. Remove the pan from the oven and scatter the chocolate chips or chopped chocolate evenly over the top. (Or melt and drizzle the chocolate decoratively over the bars after they have cooled.) Cool the bars in the pan on a rack. Run a slim knife along the unlined sides of the pan. Lift the ends of the foil liner and transfer to a cutting board. Use a long sharp knife to cut into 24 bars. May be stored, airtight, for at least 1 week.