Take the T-bone steak out of the refrigerator and let it sit at room temperature for about 30 minutes. This ensures more even cooking.
Pat the T-bone steak dry with paper towels. Season both sides generously with salt and pepper.
Heat a heavy-bottomed skillet, preferably cast iron, over medium-high heat. Add the oil to the skillet and swirl to coat the bottom evenly.
Carefully place the seasoned T-bone steak in the skillet. Let it sear without moving for about 4-5 minutes on one side until a golden crust forms. Use tongs to flip the steak and sear for an additional 4-5 minutes on the other side. Adjust cooking time based on desired level of doneness.
Reduce the heat to medium-low. Add the butter to the skillet and let it melt. Stir in the minced garlic, chopped thyme, and chopped rosemary. If desired, add a pinch of red pepper flakes for a touch of heat.
Tilt the skillet slightly and spoon the garlic herb butter sauce over the steak. Continue to baste the steak with the sauce for about 1-2 minutes, ensuring the steak is well-coated and infused with flavor.
Use a meat thermometer to check the internal temperature of the steak. For medium-rare, aim for an internal temperature of around 130-135°F (54-57°C). Adjust the cooking time accordingly for your desired level of doneness.
Once the T-bone steak reaches your desired level of doneness, remove it from the skillet and transfer it to a cutting board. Let the steak rest for about 5 minutes before slicing.
After resting, slice the T-bone steak against the grain into individual portions. Serve immediately, drizzling any remaining garlic herb butter sauce from the skillet over the steak slices.