Step 1: Set up your grill for direct grilling and preheat to high. (Ideally you’ll be using wood or charcoal.) Brush and grease the grill grate.
Step 2: Generously season the steak with salt and pepper. Place it on the grate and grill until cooked to taste, 6 to 8 minutes per side for medium-rare.
Step 3: Meanwhile, strew the garlic, rosemary, and sage leaves over the bottom of a deep dish or platter. Arrange the grilled steak on top. Pour the olive oil over it. Turn the steak a few times to coat with the garlic, herbs, and oil. Spoon the oil that gathers in the bottom of the dish over the steak. Marinate the steak in this fashion for 3 to 5 minutes.
Step 4: To carve and serve, cut the tenderloin and strip off the bone. Cut each crosswise into 1 1/2 inch thick slices. Baste with oil one final time and serve at once.