Soak the porcini mushrooms in 1 litre of boiling water for 15 minutes. Remove mushrooms from the soaking water and drain well, reserving the soaking liquid. Coarsely chop the porcini.
Place flour and shanks in a large plastic or snap lock bag and shake to completely coat. In a large pot, heat half of the olive oil over medium-high heat. Cook the shanks, in batches, turning, until browned all over. Transfer to a plate and set aside.
Place the large pot back onto medium-high heat. Add the remaining olive oil, onion, garlic, carrots, celery and rosemary, cooking for 3 minutes, continually stirring until the onion has softened. Stir in the mushrooms, chopped porcini, beef stock cubes and bay leaf, then add the tomato paste to combine. Add the red wine and reserved porcini soaking liquid. Return the lamb shanks to the pot, add extra water to cover the lamb shanks if required, and bring to the boil. Reduce heat to low. Gently simmer for a further 2 hours and 30 minutes or until the shanks are tender and falling off the bone.
Remove the lamb shanks. Increase to medium heat and reduce cooking liquid until it reaches a thick and rich gravy consistency. Strain the gravy through a sieve into a gravy boat, using the back of the ladle to extract as much flavour as possible.
Serve the lamb with Creamy mashed potato and gravy.
THE best lamb shanks ever