Porterhouse steak can be kosher, but it depends on several factors. First, the cow from which the steak comes must be slaughtered according to kosher dietary laws, known as shechita. Second, the steak must come from the forequarter of the cow, as cuts from the hindquarter are typically not kosher due to the difficulty in removing the sciatic nerve and surrounding blood vessels. Porterhouse steak is usually cut from the rear end of the short loin and thus is generally not considered kosher in traditional Jewish dietary laws. However, if there's a specific brand or butcher who adheres to kosher practices and provides kosher-certified porterhouse steak, it's possible to find kosher variants. It’s recommended to seek out certification from a reputable kosher authority to ensure the product is indeed kosher.