Place oil, herbs, salt and pepper in a food processor fitted with a metal blade or in a blender and process into a paste. Scrape down the machine once or twice to get the job done.

Place leg of lamb in a large roasting pan and coat with garlic-herb mixture all over. Let lamb sit at room temperature for 2 hours. This allows the meat to come to room temperature for even roasting and for the garlic and herb flavors to permeate the meat.

Position rack in middle of oven. Preheat oven to 350°F/180°C.

Roast lamb for an hour and check temperature with an instant read thermometer. You want to bring the lamb to 120°F/48°C for very rosy pink lamb, or about 130°F/55°C if you want it more on the medium side, as in the images. Time is less important than temperature; just roast until desired doneness is reached. Remove from oven, loosely cover with foil and allow to sit for 15 minutes before carving. Lamb is ready to serve with pan juices.