Brown Meat: Preheat the pressure cooker on "Saute/Sear" at HIGH TEMP for 1-2 minutes. Brown the lamb shanks in two batches until a rich caramel color develops. Keep the lid off during this process. Once browned, remove and set aside.
Saute Aromatics: In the same pot, sauté onion, celery, and carrots for 3 minutes. Add tomato paste, stir, and cook for an additional 3 minutes. Pour in red wine and beef stock/broth, then add whole garlic cloves and rosemary sprigs. Return the lamb shanks to the pot, nestling them into the mixture.
Cook: Secure and lock the lid. Set the valve to seal. Select "PRESSURE COOK," choose "MEAT/POULTRY," and adjust the timer to 60 minutes. Press start. After the timer elapses, release the pressure valve, remove the lid, and transfer lamb shanks to a baking tray.
Finish Sauce: Strain the liquid from vegetables into a bowl, discarding the vegetables. Heat the liquid on low for 5 minutes until it slightly reduces and thickens. Remove from heat.
Cooking the Potatoes and Beans
Potatoes: Add peeled potatoes to a pot of hot water and bring to the boil. Cook for 10 to12 minutes then test with a fork to see if soft. Once they are soft, drain thewater and mash with a potato masher. Add the milk, butter and mayonnaise until smooth and creamy.
Beans: Steam the bean in a steamer over a pot of water for about 5 minutes, or cook in a bowl of water in the microwave for 3 minutes until just cooked.
Serving
Plating up: Evenly spread the mashed potato across 4 large plate, add a lamb shank to each and drizzle on a little of the sauce, and add the green beans.
Notes
Red Wine: a cabernet sauvignon is what I use and no need for an expensive wine, a cheap one will do so long as it is still "drinkable"Don't skip the searing step: Searing lamb shanks before slow cooking enhances their flavor, creating a delicious crust and sealing in juices. This crucial step contributes to the depth of taste in the final dish.