1Combine flour, sugar, and cocoa in a medium bowl; stir well. Cut in butter with a pastry blender until the mixture resembles coarse meal. Press the mixture into a 13 x 9 x 2 inch baking pan. Bake at 350 degrees for 15 minutes; let cool on a wire rack for 10 minutes.
2Combine the condensed milk, egg, and vanilla; stir until blended. Stir in the pecans. Pour over the prepared crust. Bake at 350 degrees for 25 minutes.
3Let cool completely in the pan on a wire rack; cut into bars. Cover and store in the refrigerator.