In a medium bowl, beat the butter with a wooden spoon until creamy and smooth.
Add the herbs, shallot, and garlic, if using. Season the butter with salt and black pepper and stir until well combined.
Make the grilled beef tenderloin
Pat the tenderloin dry with paper towels. Using a sharp knife, trim any fat. Slide the blade under the long silvery membrane and remove it.
Fold about 6 inches (15 cm) of the thin flap end of the meat under the rest of the tenderloin to make it about as thick as the rest of the filet and ensure even cooking. Tie the tenderloin with kitchen string at 3-inch (8-cm) intervals.
Rub the tenderloin all over with oil. Rub with pepper, pressing it into the meat, and season with salt.
☞ TESTER TIP: Let the tenderloin rest at room temperature for 1 hour before grilling.
Prepare a medium-hot charcoal or gas grill for indirect grilling. Grill the beef over the hottest part of the grill, turning it every few minutes so a slightly charred crust develops all over, 20 to 25 minutes.
Carefully move the tenderloin to the cooler side of the grill and cook until a thermometer inserted in the thickest part of the meat registers 120°F (49°C) for rare and 130°F (54°C) for medium-rare, 7 to 12 minutes.
Let the beef rest on a cutting board for at least 20 minutes. Snip off the string, slice the meat, and serve on a platter, or plated and topped with a smear of compound herb butter.
Notes
Internal temperature--To avoid tough beef, don't cook past an internal temperature of 145°F. For rare to medium-rare beef, aim for an internal temperature of 125°F.
Get ahead--The beef can be prepared, seasoned, and tied up to 36 hours before cooking. Store in the refrigerator.
Storage--Leftovers can be stored in a sealed container in the refrigerator for up to 3 days.
Dietary--This recipe is suitable for gluten-free and dairy-free diets.