Fish pot pie

2 tbsp rapeseed oil

1 onion, finely chopped 

2 small leeks, trimmed and thinly sliced 

4 tbsp dry white wine 

400ml cream 

675g mixed skinned and boned fish fillets, cut into bite-sized pieces (such as trout or salmon, hake and smoked cod or haddock) 

 225g raw peeled tiger prawns, thawed if frozen 

100g frozen peas 

2 tbsp chopped fresh flat-leaf parsley

pinch of cayenne pepper 

1 × 320g ready-rolled puff pastry sheet, thawed 

1 egg, beaten with a pinch of salt sea salt and freshly ground black pepper 

To serve:

lightly dressed rocket