The ling, redfish, hake and pollock are more than adequate substitutes for cod. The classic preparation method is boiling. The cod should be firm on the bone and the outer portions of meat not too soft, so that it reaches the plate whole without falling apart.
Cod meat is very delicate. The best flavour is obtained if, after cooking, small white particles (the protein) are visible. This is an indication that the fish is extremely fresh.