Place the shanks on a large board and sprinkle liberally with sea salt and black pepper. Crush the juniper berries, then sprinkle over as well.
Heat the butter and a glug of oil in a large casserole pan and brown the meat on all sides, in batches if necessary. Remove the shanks from the pan and set aside.
Peel and finely slice the onion, then trim and slice the celery. Add both to the pan and reduce the heat to low. Cook for 10 to 15 minutes, until softened but not coloured.
Add the currants to the pan with the wine and bring to the boil, then simmer for a few minutes. Return the shanks to the pan with the rosemary and stock and bring back to the boil. Reduce the heat and leave to simmer, covered, for 4 hours or until the meat is falling off the bone.
Remove the shanks and set aside. Bring the sauce back to the boil and cook on a medium heat until thick and glossy. Shred the meat off the bones; when the sauce thickens, return the meat to pan and heat through. Serve with neeps 'n' tatties.