Leg of lamb is a traditional and impressive French Easter dish. Though, it can definitely be enjoyed at any other occasions.
Make all the prep a day ahead. For a more tender and moister piece of meat, it needs to be taken out of the refrigerator before cooking. If a 10 ounces/300g steak needs 30 min to warm up, a 3kg/6.lb roast would have to be left out three hours.
Duck fat can be subbed for oil. Mix duck fat with thinly chopped rosemary, thyme and crushed garlic – set aside.
Pat dry the leg with paper towels. To french it, using a sharp boning knife, cut straight into the bone about 1.5-inch/3.5cm from the end, moving the knife all around the bone. Scrap out meat pulling it away using your knife and paper towel. Prior to tie up meat with bucher twine, season the open parts of the meat with the herbed seasoning, salt and pepper.
Depending on what the leg of lamb looks like, you may need to truss it. It helps retain its shape while it cooks in the oven and stops the meat from spreading. Just tie a series of interlinked knots to secure the meat in place; it doesn't have to be perfect. Rub the whole leg with remaining rosemary-garlic seasoning. Some of the garlic cloves may also be inserted into the roast if desired using the tip of your paring knife. Cover roast with foil and refrigerate overnight.
Quarter onions and peel. Wash and peel carrots and cut into chunks. Split garlic head in half – refrigerate until ready to use.
Scrub potatoes and wash. Cook potatoes in salted water* for about 25 minutes or until just cooked through – do not overcook!. Drain and spread potatoes onto a tray lined with paper towels to cool off. Trimming haricots verts is quick. Just gather small bundles with all of the tough stem ends facing in one direction, and cut just below the stem. To parboil haricot verts, in a large saucepan bring water to a boil and salt generously. Cook beans for about 7 min – transfer in ice water and drain. Store in a large container lined with paper towels. Store haricot verts in the refrigerator until ready to use. Parboiled green beans can be kept up to 5 days in the refrigerator.
In order to get a more tender and moist meat, remove roast from refrigerator about 3 hours to allow it to come closer to room temperature before cooking. Take the foil out and remove excess garlic and add it to the veggies. Transfer the leg of lamb to a greased wire rack and use the baking tray for the onions, carrots and garlic. Add salt and white wine. Season lamb with salt and pepper on all sides. Turn oven on to 390ºF/200ºC. Lower temp to 350ºF/180ºC if using a convection oven. Place the leg of lamb on top of the rack in the oven and place the veggies underneath so that some of meat juice will be dripping over during cooking. Cook for lamb for 90 minutes or until internal temperature reads 135ºF/57ºC for medium rare. Keep in mind that temperature continues to rise 5ºC at least once meat is removed from the oven. Always stick the thermometer into the thickest part of the meat without touching the bone. Cook 30 minutes more for medium well. Rotate roast and veggie tray half way through. Remove roast and place rack onto another tray for the juice to drain. Let rest for 30 min or more before carving. This allows the juice to redistribute. Once the meat has rested, remove the string from the exterior of the roast.
Save carrots, onions and roasted garlic and set aside. In the same baking tray – add stock, stir that up and transfer the whole thing to a saucepan. Bring to a boil and sieve – reduce gravy on low heat until desired consistency. Add the rendered lamb juice from resting. Readjust seasoning with salt and pepper if needed. Sauces can be finished with butter, to luxurious effect, with a technique called montée au beurre. Add pieces of cold butter to the heated sauce and rotate the pan steadily, allowing the butter to emulsify slowly. Do not boil.
*Potatoes can also be seasoned with fat, herbs, salt and pepper and being directly oven-roasted at 425ºF/220ºC for about 35 min. If so, put potatoes in the oven as soon as the lamb is out. Otherwise, season boiled potatoes and sear them in a large frying pan. Transfer the finished potatoes to a baking tray and keep warm.
By the time potatoes are roasting, sautée green beans in a hot frying pan with the fat. Season with salt and pepper and sautée for 3 min on high heat. Add garlic and continue to cook until fragrant. Add parsley and remove from the heat.
In a warm and beautiful large plater, arrange potatoes, green beans and roasted veggies and top with the roast. Carve the meat using a slicer. Season with salt and pepper if desired. Leftover lamb meat can be enjoyed with mustard, cornichons and bread. Save the bone for you next soup, bean stew or lamb stock. Enjoy!