Pat the porterhouse dry with paper towels
Season generously with salt and black pepper
Let it sit at room temperature for 30 to 45 minutes
Preheat a cast-iron skillet or grill to high heat
Add a small amount of high-smoke-point oil if using a skillet
Sear the steak for 2 to 4 minutes per side
Sear the fat edge and bone side briefly
Reduce heat or move to indirect heat to finish cooking
Cook to desired doneness using a meat thermometer
Remove at 125°F for rare
Remove at 130°F for medium-rare
Remove at 140°F for medium
Rest the steak for 10 to 15 minutes
Slice against the grain
Separate the strip and tenderloin if desired before slicing
Serve immediately