• Remove the lamb from the fridge and allow it to rest at room temperature for a minimum of 30 minutes.  
• Preheat your oven to 400 °F (200 °C) and prepare the middle rack of your oven.
• Wash the leg of lamb under running water and trim some of the excess fat and skin but not all of it.
• Prepare the seasoning. Mix salt, pepper, dry oregano, olive oil, lemon juice, and mustard. Set aside.
• Peel 6 garlic cloves. Use a sharp knife to make slits all over the leg of the lamb and insert a garlic clove into each one.
• Apply the seasoning. Use a tablespoon to coat the leg of lamb with the seasoning on all sides.
• Add two cups of water (or chicken broth) to the bottom of the roasting pan. Don't pour water over the meat because it will wash away the seasoning.
• Prepare the potatoes. Peel the potatoes and cut them in half lengthwise and then in quarters. For small to medium-sized potatoes, quarter them, and for larger ones, cut them into six wedges.
• Place the potatoes into a bowl and cover with water. Rinse and drain a couple of times until the water is clean. Set aside.

ROASTING

If the cut of lamb weighs less than 4-5 lbs (1.8-2.3 kg)

• Drain the potatoes and season with salt, pepper and oregano. Use a spoon or your hands to coat them well. Place the lamb in the roasting pan. Scatter the potatoes around the lamb, and cover the pan with a lid. If there is no lid wrap the roasting pan with parchment paper and aluminum foil.
• Place the roasting pan in the middle rack of the oven and cook for 20 minutes to 400 °F (200 °C), then reduce the temperature to 360°F(180°C).
• Adjust the roasting time according to your desired level of doneness (rare, medium, well-done). See the guide in the post above.
• Remove the pan from the oven 20-30 minutes before the total roasting time. Increase the oven temperature to 400°F (200°C). Uncover the lamb. Toss gently the potatoes gently.
• If there is not enough liquid, add some hot water (if necessary). Return the pan to the oven for the last 20-30 minutes until the skin is brown and crisp and the potatoes soft.

If the cut of lamb weighs more than 5 lbs (2.3 kg)

• Place only the lamb in the roasting pan. Don't add the potatoes (keep them in the water). Cover the pan with a lid. If there is no lid wrap the roasting pan with parchment paper and aluminum foil.
• Place the roasting pan in the middle rack of the oven. Cook for 20 minutes to 400 °F (200 °C), then reduce the temperature to 360°F(180°C).
• After 1 hour, prepare the potatoes. Drain them and season with salt, pepper, and oregano. Use a spoon or your hands to coat them well.
• Scatter the potatoes around the lamb, cover the pan again (with the lid or parchment paper-foil wrap), and return it to the oven. Adjust the roasting time according to your desired level of doneness (rare, medium, well-done). See the guide in the post above.
• Remove the pan from the oven 20-30 minutes before the total roasting time. Increase the oven temperature to 400°F (200°C). Uncover the lamb. Toss the potatoes gently.
• If there is not enough liquid, add some hot water (if necessary). Return the pan to the oven for the last 20-30 minutes until the skin is brown and crisp and the potatoes soft.

If the cut of lamb weighs more than 7 lbs (3.2 kg)

• Follow the previous steps (lamb that weighs more than 5 lbs/ 2.3 kg).
• The potatoes need about 1 to 1 ½ hours to become soft. If the cut is too big you should adjust the time you add the potatoes to the roasting pan. They will be mushy if you roast them for more than 1 ½ hours. 

SERVE

• Allow your lamb to rest for at least 15 minutes before carving.