Position racks so that the cake will bake in the middle of an oven and preheat the oven to 350° F. Grease a 13-by-9-inch pan as directed [see below]; do not line or flour it. Set aside.

Toast the pecans as directed [see below], then chop and set aside.

Place the flour, sugar, cocoa, baking soda, and salt together in a strainer or sifter and sift into a bowl. Whisk to mix well. Add 2 cups water, the oil, vinegar, and vanilla, and whisk or beat with an electric mixer just until the ingredients are well blended.

Scrape 3 cups of the batter into the prepared pan and smooth the surface with a rubber spatula. Bake until the top is just set, about 15 minutes.

Remove the pan to a work surface. Sprinkle the chocolate chips and toasted pecans evenly over the partially baked cake, then drizzle evenly with the Caramel Sauce. Cover with the remaining cake batter and smooth the surface. Bake until the cake feels firm when lightly touched in the center with your fingertip and a skewer inserted into the center of the cake comes out moist but not gooey, about 35 minutes longer.

Remove the pan to a wire rack to cool completely.

Cut into narrow slices, as shown in the photograph, or squares and serve directly from the pan.