In a large heavy bottomed pot over medium heat, brown lamb shanks for 5 minutes per side. Add leeks, celery, carrot, garlic, salt, bay leaf and seasoning then cook for 5 minutes stirring once or twice. Add mushrooms, stock and Worcestershire sauce and herbs then place a lid on and simmer for 2 ½ to 3 hours until the lamb is very tender. If the liquid evaporates too much during cooking, top it up with some stock or water.
Remove lamb shanks from the pot, pull all meat from the bone and set aside. Strain the broth or remove the bay leaf then puree everything using an immersion blender for a richer broth. Make a slurry with the cornstarch and water, whisk into the pot and stir until thickened. Add the pulled lamb back into the gravy, add apple cider vinegar and season to taste. Set aside until ready to assemble.
Cut the potatoes into fries and soak in cold water for 10 minutes. Strain and drain on a clean kitchen towel, patting dry. Add fries to a bowl or sheet pan and toss with olive oil and salt then air fry for 15-20 minutes at 375F depending on thickness.
To bake: Preheat your oven to 375F and spread the fries evenly in a single layer on the sheet pan. Cook for 20 minutes, turn the heat to 425F and continue baking until crisp (about 10-20 minutes). The time will depend on the thickness of your fries, so watch it halfway through and test for doneness.
To assemble: Place fries on a plate, add cheese curds and spoon a few ladles of lamb gravy over. Finish with fresh herbs and pepper. Serve immediately.