Remove the porterhouse steak from refrigerator 30-60 minutes before cooking to let it reach room temperature. This promotes even cooking for the juiciest steak.
Position the oven rack in the middle and preheat oven to 425°F (218°C).
Place a large cast-iron skillet over high heat and allow to heat for 5 minutes until extremely hot. (You can also place in the preheated oven for 15 minutes.)
Pat dry the steak with paper towels to remove excess moisture that could interfere with searing.
Rub 1 tablespoon of olive oil on both sides.
Season both sides with salt and pepper.
Add the remaining 1 tablespoon oil to the pan and swirl to coat.
Carefully place the porterhouse in the pan using kitchen tongs, laying it away from you to avoid splatter.
Sear the first side for 2 minutes.
Flip using kitchen tongs and sear the other side for 2 minutes.
Add garlic, butter and fresh herbs to the pan. Then immediately transfer the skillet to the oven.
Bake without flipping the steak according to your desired doneness: 1-2 minutes for rare, 2-3 minutes for medium-rare, 3-4 minutes for medium, and 5-6 minutes for well-done. Check doneness using an instant-read thermometer***.
Remove steak to a plate or cutting board covered with aluminum foil to rest for 5 minutes so the juices can retreat back into the meat.
To serve, cut the meat away from the bone and slice across the grain into strips.