A porterhouse is a large t-bone. The T in t-bone is from a vertebrae that has been sawed in half. The little hole at the top of the T is half of the foramen, and this is where the spinal cord passes through the bone. Straight down from there is the transverse process, which divides the two pieces of meat. The chunks of meat, when deboned and removed, are the short loin (New York strip) and the tenderloin (filet mignon). When you compare a porterhouse to a t-bone, you will notice that the smaller side—that is to say the tenderloin side—is bigger. So, when you buy a porterhouse, you get more tenderloin for not much more money.
When shopping for porterhouses, keep in mind that according to the USDA the width of the tenderloin must be at least 1.25 inches in order for it to be sold as a porterhouse instead of a t-bone.
1. Let your steaks warm up a bit. Meat should almost always be cooked from room temperature. It helps the meat cook evenly. Just take the steaks out of the fridge an hour before you want to start cooking them. Unwrap them and set them on a plate or cutting board. You can season them now or wait until later. Waiting will make little difference. I wouldn't season anymore than an hour in advance, though. Preheat the grill for at least 10 minutes before you put the steaks on.
2. Season the steaks simply with salt and pepper. This meat is some of the tenderest and most expensive meat available. It is expensive because it is so tasty, tender, and delicious. So don't go and ruin all that flavor by seasoning it with a bunch of strong flavors. Stick to sea salt and fresh-cracked black pepper. Rub the seasoning in with your hands to make sure you get it on every bit. Finally, add a thin layer of some safflower, canola, or other vegetable oil.
3. Once the grill is preheated, lay the steaks on the grill. Assuming that your grill is a gas grill, cook your steaks over high heat if you want them rare. The high heat will cook the outside faster and leave the inside bloody. If you want your steaks cooked more than rare, lower the heat medium-high. Lay the steaks on the grill either parallel to the grates or 30 degrees perpendicular to it. The picture shows that the first steak is parallel and the second is 30 degrees perpendicular.
4. Rotate the steaks 30 degrees in either direction. After 2 minutes of grilling time, rotate the steaks. The reason we rotate the steaks is to establish grill marks. If you have unused grill space, rotate and move the steaks to that space. The grate is hotter there, and moving them onto the heated grills will leave clearer grill marks. After 2‒3 minutes, you should see some brown creeping up the sides of the steak. If you want rare, flip them now. If you want it cooked more, wait a few more minutes.
5. Flip the steaks to grill the other side. If you are satisfied with your grill marks you won't have to rotate this side. I check my steaks by poking them with my finger. In order to give you some idea of what you are feeling for, I have described below a method for you to learn what rare steak versus medium steak feels like. The steak on the right was cooked to medium. A trifle too much, in my opinion, but it was for someone else. Of course it was still pretty darn good. It just wasn't as juicy as it could have been.
I am sure you have all heard of the thumb reference for cooked meat. To tell you the truth, I never thought it was all that reliable of a method until I heard it described to me in this way. Hold your hand up with the palm facing you. Now touch the tip of your thumb to the tip of your pointer finger, just so they are touching with just a little pressure. Now, with your other hand's pointer finger, poke the meaty, muscly part (at the base) of your first hand's thumb. That is what rare meat should feel like. And when you touch the tip of your thumb to the next finger, the middle finger, press that same place on your thumb again. That represents medium. As you progress down toward the pinky you will notice it begins to get very firm. The ring finger would be around medium-well, and the pinky would represent well done. As you cook meat, continue to practice this technique and eventually you will just know, like I do.