Pour the beef broth into the bottom of the roasting pan. This will help keep the lamb moist during cooking.
Cover the roasting pan tightly with aluminum foil, ensuring it's sealed around the edges.
Place the pan in the preheated oven and roast the lamb for approximately 1 hour.
After 1 hour, remove the foil covering from the roasting pan.
Increase the oven temperature to 425°F (220°C) and continue roasting the lamb for an additional 15-20 minutes or until the surface is golden brown and the internal temperature reaches your desired level of doneness. For medium-rare, aim for an internal temperature of 145°F (63°C), and for medium, aim for 160°F (71°C).
Once done, remove the lamb leg from the oven and let it rest for about 10-15 minutes before carving. This allows the juices to redistribute, resulting in a juicier and more tender roast.
Carve the roasted lamb leg into slices, against the grain for optimal tenderness.