To make this beef tenderloin, start by preheating your oven to 275 F.
Next, line a baking sheet with tin foil and place the beef tenderloin on top of it.
Use your hands to rub half of the kosher salt onto the beef tenderloin and set it aside.
Next, prepare the marinade by whisking together the olive oil, mashed garlic, chopped rosemary, chopped thyme, onion powder, ground black pepper, and remaining kosher salt in a small bowl. Taste and adjust the seasonings as needed.
Then, rub the marinade all over the beef tenderloin, ensuring that all sides are covered in the marinade.
Insert a meat thermometer into the meat, if using. If you opt to not use a meat thermometer, see the recipe notes!
Finally, place the tenderloin into the oven and allow it to cook until it reaches your desired internal temperature. For rare, this is approximately 130 F, or 50 minutes in the oven. For medium rare, this is approximately 135-140 F, or 1 hour and 10 minutes in the oven.
Once the meat has cooked to your desired temperature, remove it from the oven and allow it to rest for 10 minutes before slicing. Then, serve and enjoy!