Recipe video above. A 3-hour lamb shoulder is great. A 12-hour lamb shoulder is better! The meat is even more succulent because a lower cooking temperature means less moisture loss, and better flavour infusion from the rub. The sauce is a Lamb Jus made using the braising juices so it has phenomenal flavour. Don't be intimidated, it's simple and no more difficult to make than gravy!This is an excellent make-ahead recipe for gatherings. Why? Because you can make up to 4 shoulders in one standard oven. And the room for error is also almost nil; it's almost entirely hands-off cooking that magically takes care of itself overnight. Most importantly, the meat is so juicy it reheats 100% perfectly. I cook it overnight and reheat to serve that evening.About scaling up: 2 shoulders can be cooked in one large pan with no change to cook time. 4 shoulders (2 lambs in 2 pans, on 2 shelves) takes about 14 to 15 hours.
Marinade/rub: Mix the Marinade ingredients in a small bowl. Rub all over the lamb surface, getting it right into all the cracks and crevices!
Marinate 2 - 24 hrs: If time permits, marinate for 2 hours on the counter in a roasting pan, or up to 24 hours in the fridge. I skip this step more often than not, however. (Note 4)
Prepare roasting pan: Scatter onion in the base of the roasting pan. Place lamb shoulder on top . Pour water into pan.
Roast uncovered for 45 minutes.
Slow-roast 12 hours: Turn oven down to 100°C/210°F (both fan and standard, Note 5). Cover lamb with baking paper, then a double layer of foil and seal very tightly to avoid water evaporation. Roast for 12 hours (I always do overnight!).
Check meat – Test side of lamb with two forks. The meat should be fall-apart tender. If not, cover and return to oven.
Remove lamb: There will (should!) be a lot of liquid pooled under the lamb in the roasting pan. Remove lamb to a large dish. Cover loosely with foil to keep warm. It will stay warm for 2 to 3 hours. See Note for reheating / making ahead.
Reduce liquid: Strain all the liquid in the roasting pan into a saucepan (Note 2). Bring to a boil then simmer rapidly on medium-high until it reduces down to 1 cup (250ml).
Thicken: Mix cornflour with water. Pour into jus in a thin stream while stirring continuously. Continue to cook for a minute or two over medium heat, stirring every now and then, until it thickens to a syrup consistency. Add salt and pepper to taste.
Serve Slow Roasted Lamb with Jus. Use tongs for tearing meat off - no knife for carving needed! Pictured in post with Greek Lemon Roasted Potatoes, a perfect match for this Greek-ish flavoured lamb. Roasted Vegetables would also be ideal.
Serving portions - Allow 300g/10oz of lamb per person for normal people, or 500g/1lb for big eaters. This measure is the bone-in, raw lamb. Meat shrinks considerably once cooked, you probably lose around 30% in weight so ends up being much less as cooked meat.1. Lamb shoulder - A tough cut of meat that needs to be cooked far beyond well done until the meat becomes fall-apart tender. You do not need a knife to carve this meat, pull it off with tongs!Shoulder comes in all sorts of sizes depending on the size/age of lamb! The cook time doesn't really differ because the meat itself needs a minimum amount of time to break down and become tender, and also the low temperature means it's very forgiving, ie. it's hard to overcook this meat to the point it dries out.If your shoulder is really small though, say 1.2kg / 2.4lb, then you can probably cut down the cook time by 2 hours, but it should still be succulent even if you stick with the full 12 hours.Lamb leg - This recipe is not suitable for leg, please use this Slow Roasted Lamb Leg recipe instead.2. Water is all we need for the braising liquid because it gets so much flavour from the lamb juices, no need to use stock.Liquid in pan after slow roasting - If the foil was tightly sealed (and your lamb is juicy!), you will/should end up with 3 - 4 cups liquid at the end. If you have less than 1 cup, add water to top up before simmer on stove to make the Jus.3. Onion - Elevates the lamb slightly off base for more even cooking, plus adds flavour to the liquid that forms the Jus (sauce). Can keep skin on because it holds together better and we strain it out anyway.4. Marinating - The long and slow cook time means the lamb is essentially marinating as it cooks, in my opinion. But I'm sure people with a more refined palate than me can probably taste the difference between marinating, and not. (I can't).5. Oven temp - I find that you need to use the same temperature for standard vs fan oven for low temperature, slow cooking. It's something I've discovered over the years across various recipes, including things slow cooked at slightly higher temperatures like Massaman Lamb Shanks. I think it's because the lower the oven temperature, the smaller the difference in actual oven heat between fan vs standard ovens.6. Workflow / timing / reheating: Here's what I do -
Serving for lunch - Slow roast overnight so it comes out of there oven around 9 am (to give a bit of headroom for extra oven time if needed, in case meat is not fall-apart-tender). Lamb will stay warm covered in foil for 3 hours easily, in a new pan or container (don't leave in liquid, as it will continue cooking). If needed, reheat per below.
Dinner - Slow roast overnight, allow lamb to cool to room temperature, then store in fridge. Take out 3 hours prior to serving (to de-chill for more even, faster reheating). Reheat covered in oven at 150°C/300°F for 1 hour (for 1 lamb shoulder; 4 will take longer). Emergency reheating option: Microwave it. Yes, really!
Jus - Make, cool to room temperature, then refrigerate until required. Reheat in microwave or saucepan on stove.
Storage - Cooked lamb will keep in the fridge for 4 to 5 days, or freezer for 3 months. It is at its best within 24 hours of cooking I find, but it's still 97% excellent on days 2 to 5.