Let the beef tenderloin sit at room temperature for 1-2 hours before cooking. This helps it cook evenly.
Preheat your oven to 425°F (220°C).
In a mixing bowl, combine the softened butter, minced garlic, chopped rosemary, and thyme to create the garlic herb butter mixture.
Trim any silverskin from the tenderloin, tuck the thin end under, and tie the tenderloin with kitchen twine to guarantee even cooking.
Heat the avocado oil in a cast-iron skillet over medium-high heat. Once hot, sear the tenderloin on all sides until a golden crust forms, about 10 minutes.
After searing, spread the garlic herb butter mixture over the tenderloin.
Transfer the skillet to the oven and roast the tenderloin for 15-20 minutes, using a meat thermometer to check for doneness.
For medium-rare, remove the roast from the oven when it reaches 120°F (the resting temperature will be 125-128°F). Let it rest for 10-15 minutes before slicing.