Optional: Remove the porterhouse steak from refrigerator one hour ahead of time. This will take the chill off to promote even cooking for the juiciest steak.
Preheat the oven to 425°F (218°C), placing the oven rack in the upper middle position.
Place the steak on a work surface. Pat dry both sides with paper towels to remove excess moisture that could interfere with searing.
Rub the steak on all sides with 1 tablespoon of oil. Then rub the salt and pepper on all sides. (You can adjust the salt to taste, but will need a good half teaspoon to get tender steak.)
Place a large ovenproof skillet*** over high heat. Allow it to heat for 4 to 5 minutes until very hot and ensure your kitchen exhaust fan is turned on. (Another option is to place the skillet in the preheated oven for 10 minutes.)
Using kitchen tongs, carefully place the porterhouse in the pan. Let it sear undisturbed for 2 minutes. Then flip and sear the other side for 2 minutes. (Use oven mitts to avoid burns, as the pan handle will be hot.)
Add the minced garlic, butter and fresh herbs to the pan. Immediately transfer the skillet to the preheated oven and close the door.
Bake until the steak reaches your desired doneness. Start checking the internal temperature of the meat after 5 minutes by inserting an instant-read thermometer an inch away from the bone. Rare is 125°F / 52°C, Medium-rare is 130°F / 54°C, Medium is 140°F / 60°C, Medium-well is 145°F / 62°C, and Well-done is 155°F / 68°C or more.
Remove the steak to a cutting board. Cover with aluminum foil to keep warm. Let it rest undisturbed for 5 to 10 minutes to let the juices redistribute. (Avoid cutting into the meat as juices will escape and make the steak tougher.)
To serve, cut the meat away from the bone. Then slice across the grain into strips.