Place a large sauce pan on the heat when red hot add the sliced shallots, fresh mussels and white wine, place a tight fitting lid on and cook for 2-3 minutes until the mussels start to open, remove from the heat and strain the cooking juices into another sauce pan.
Let the mussels cool and then take all the meat out of the shells and reserve. Finely dice the carrot, celeriac and potato and place in mussel cooking juice.
Return to heat and boil for 10 minutes until the vegetables are al dente. By this time the juices should have reduced by half.
Add the cream and curry powder and bring to the boil.
Peel the parsnip into long strips and place the strips a few at a time into a deep fat fryer until golden and crispy. Remove onto kitchen paper and sprinkle with a little salt and ground cumin, place to one side.
Brush the mackerel fillets with a little rapeseed oil and season with sea salt and freshly ground white pepper. Place on a tray skin side up and cook under a hot grill for 3-4 minutes until the skin is crispy. Remove from the grill and rest for a couple of minutes and the residual heat will cook the fillets through. Finish with a squeeze of fresh lime.
Add the mussel meat back to the creamed curry broth and heat back through.
Finish the sauce with some chopped fresh coriander.