In a small bowl, combine minced garlic, fresh rosemary, fresh thyme, dried rosemary, dried thyme, salt, and pepper to create a classic flavor blend.
Rub the mixture all over the boneless leg of lamb, ensuring it's evenly coated. Let it rest in the refrigerator overnight, uncovered, on a sheet pan fitted with a wire rack.
Preheat your oven to 200ºF.
Place the rested lamb on a foil-lined sheet pan fitted with a wire rack.
Slow-roast the lamb in the preheated oven until it's about 10 degrees away from your desired internal temperature. 1.5-2 hours for medium.
Remove the lamb from the oven and let it rest tented with foil.
Increase the oven temperature to 400ºF (or use the broil feature) and cook for an additional 10 minutes to crisp the exterior just before serving.
Remove from the oven and let the lamb rest for at least 10 minutes before carving.
To serve, place the lamb on a cutting board with the fat side facing up and take note of the direction of the muscle fibers (grain) in the meat. When slicing, cut perpendicular to the direction of the muscle fibers (against the grain) to ensure each slice is tender and easy to chew. Start from the shank end (thinner end) and work your way towards the thicker end, making horizontal slices across the lamb. Aim for slices that are about 1/4 to 1/2 inch thick.