Porterhouse steak is a tender and juicy cut of beef. When purchasing a porterhouse, look for marbling throughout the steak. Marbling is thin veins of fat that can be seen. Marbling gives the porterhouse steak added flavor. A good marinade should compliment the steak and bring out its natural flavors, not over power the steak. Never marinade a porterhouse steak for longer than 12 hours.Marinades help the meat fibers breakdown so render the steak more tender, a steak left in a marinade to long can lose its texture.
Place all the ingredients in a bowl and whisk until blended.
Place the steak in a container or a large zip lock bag. Pour the marinade over the steak and place it in the refrigerator for 4 to 12 hours. Do not marinate for more than 12 hours or the fibers in the porterhouse steak will break down and lose its texture.
Remove the steak from the refrigerator, pat dry and let it sit for 30 to 45 minutes. The steak should be close to room temperature before it cooked. This will allow for better searing to lock in flavor. If additional moisture is noticed prior to cooking, blot with a paper towel.
Prepare the grill. If using a gas grill, place one burner on hi and the other on medium-low. If using a charcoal grill, use coals only on one side of the grill.
Place the steak on the hot side of the grill and sear for two minutes on both sides. Move the steak to the cooler section of the grill. Cover and let cook for eight minutes for medium rare or longer if a more well-done steak is desired.