How to Make It
Place oil, garlic, shallots, salt, pepper, coriander, and dill in a mini food processor; process until a mostly smooth loose paste forms, about 30 seconds.
Pat turkey dry with paper towels, and place on a rimmed baking sheet. Loosen skin from breast by inserting fingers, gently pushing between skin and meat. Rub half of spice paste under loosened skin; rub remaining spice paste into skin on outside of turkey. Chill, uncovered, at least 8 or up to 12 hours.
Fill a pellet container to an electric pellet grill with hardwood pellets according to manufacturer’s instructions. Set temperature to 225°F, close lid, and preheat pellet grill 10 to 15 minutes.
While grill preheats, let turkey stand at room temperature. Stir together butter, thyme, and rosemary in a small bowl. Place turkey on grill grate, close lid, and grill, brushing with herb butter every hour, until a meat thermometer inserted into thickest portion of turkey breast registers 150 °F, 4 1/2 to 5 1/2 hours. Transfer turkey to a cutting board; let rest 45 minutes before carving.