Millionaire’s Shortbread

Line a 9-by-13-inch baking pan with 2 long sheets of foil, laid perpendicular to each other in the pan. Push the foil into the corners and up the sides of the pan, smoothing it flush to the pan.

Combine the flour, sugar and salt in a medium bowl. Add the melted butter and stir with a rubber spatula until the flour is evenly moistened. Crumble the dough evenly over the bottom of the prepared pan, then use your fingertips and the palm of your hand to press and smooth the dough into even thickness. With a fork, pierce the dough at 1-inch intervals. Bake until light golden brown and firm to touch, 25 to 30 minutes. Using a sturdy metal spatula, press on the entire surface of the shortbread to compress it (this will make the finished bars easier to cut). Cool the crust until it is just warm, about 20 minutes.

To make the filling: Stir all the filling ingredients together in a large, heavy saucepan. Cook over medium heat, stirring often, until the mixture registers between 236 and 239 degrees on a candy thermometer, about 16 to 20 minutes. Pour the caramel over the crust and spread it to even thickness. Let cool completely, about 1 ½ hours.

To make the chocolate layer: Microwave the chocolate chips in a bowl at 50 percent power, stirring every 15 seconds, until the chocolate is melted but not much warmer than body temperature, 1 to 2 minutes. Spread the chocolate evenly over the surface of the caramel. Refrigerate until the chocolate is just set, about 10 minutes.