Preheat oven to 180C. Par boil the diced potato in salted water, until it has softened slightly but not completely cooked. Then drain off and leave to cool.
Add the haddock fillets, onions, peas, broad beans, créme fraiche and nutmeg and mix everything together in a big bowl with a good pinch of salt and pepper.
Spoon the mix into a ramekin leaving a small gap at the top. Mix the Parmesan and breadcrumbs together and sprinkle across the top to cover.
Cook in the preheated oven for 20 mins and serve.