Firstly make the creamed leeks. Chop the leeks finely, and clean. Sweat in a saucepan with a little oil. When soft, add the peas, cream and mustard.
Add salt and freshly ground black pepper and cook on a medium heat for a few more minutes. This can be done in advance and heated up just before serving.
Coat the monkfish (Cod, Pollock or any firmed flesh white fish can also be used) in flour. Heat oil in a frying pan and fry the fish for about 7-9 minutes, turning as necessary. Heat up the leeks and divide between 4 plates. Place fish on top and serve with sauté potatoes.