• Combine the garlic, rosemary, salt and pepper in a bowl.
• Pat the roast dry with paper towels and sprinkle evenly with salt mixture.
• Wrap the roast with plastic wrap and refrigerate for 18 to 24 hours.
• Punch fifteen 1/4-inch holes in the center of the roasting pan, which should be about the size of the roast, and set aside.

For a charcoal grill:

• Open the bottom grill vents completely.
• Light a large chimney starter half filled with charcoal briquettes (50 briquettes; 3 quarts).
• When the coals are hot, spread them in an even layer over one-third of the grill.
• Set the cooking grate in place, cover and open the lid vents halfway. Heat the grill until hot, about 5 minutes.

For a gas grill:

• Turn all burners to high, cover and heat the grill until got, about 15 minutes.
• Turn the primary burner to medium and turn off the other burners. (Adjust the primary burner as needed to maintain the grill temperature around 325 degrees F.)

Once Your Grill is Ready

• Clean and oil the cooking grate.
• Place the roast on the hotter part of the grill and cook (covered if using gas) until well browned on all sides, about 10 minutes, turning as needed.
• Place the roast in the pan over the holes and transfer the pan to the cooler part of the grill.
• Cover (positioning the lid vents over the meat if using charcoal) and cook until the roast registers 125 degrees F on an instant-read thermometer (for medium-rare), 40 to 60 minutes, rotating the pan halfway through.
• Transfer the roast to a wire rack set over a rimmed baking sheet, tent loosely with foil, and let rest for 20 minutes. Transfer the roast to a carving board and cut across the grain into thin slices.