How to Make It
Remove roast from refrigerator 1 hour before you plan to cook. Prepare a Big Green Egg® or other charcoal grill for indirect heat with a drip pan at 350°F.
Combine butter, olive oil, basil, tarragon, rosemary, and thyme in a small bowl. Sprinkle with salt and pepper. Reserve about 1/4 cup butter mixture.
Use a paring knife to cut several holes on both sides of roast; insert sliced garlic into holes. Sprinkle roast generously on all sides with salt and pepper. Spread butter mixture all over roast, applying the heaviest layer to fat cap.
Place roast, fat side up, on grill grate and cook until a thermometer inserted deep into center of roast registers 120°F, about 2 hours. Transfer roast to a platter; tent loosely with aluminum foil, and let stand 20 to 30 minutes.
Spread reserved butter mixture on a cutting board; place roast on top. Slice roast between the bones.