An electrical resistance spot welding electrode is disclosed for contact with a narrow or other selected spot weld region in a steel workpiece in a stack-up with an aluminum alloy workpiece for use in a spot welding method in which the weld nugget is carefully formed in the aluminum workpiece at the interface of the stack-up. The welding face of the welding electrode for contact with the steel workpiece is shaped with an aspect ratio greater than one, which fits against the contact surface of the steel workpiece, while the welding face for the aluminum-contacting weld electrode is circular (with an aspect ratio equal to one). The stack-up of workpieces may include a single steel workpiece facing two aluminum workpieces in a sandwich type stack-up or two steel workpieces facing a single aluminum workpiece with the outer steel workpiece having the narrow contact surface for the steel welding electrode.