1. Use a sharp knife to trim the edges or ask your fishmonger to do this for you.
2. Place the flour into a shallow dish and season to your personal taste with sea salt and freshly milled black pepper.
3. Break the eggs into a bowl, beat well and then pour into another shallow dish.
4. Cut the lemon into large wedges such that they can give out some lemon juice when squeezed, removing any pips.
5. Wash and dry the watercress and pre-heat the oven to 160°C (Gas Mark 3).
6. Heat enough oil in a heavy-based frying pan to shallow fry the plaice fillets over a medium heat.
7. Pass the plaice through the beaten egg, making sure they are well coated and then into the seasoned flour, again making sure the fish is well coated.
8. Carefully lay the plaice fillets into the hot oil and after about 2–3 minutes, carefully turn the plaice fillets over and cook on the other side for a further 2–3 minutes, until golden in color.
9. Remove the plaice fillets from the frying pan and onto a baking tray.
10. Place into the pre-heated oven to keep warm until all plaice fillets are cooked, to avoid crowding the frying pan in any one go.
11. When all the plaice fillets are cooked, carefully lay onto warmed plates and garnish with a nice small bunch of watercress and a good size lemon wedge and serve immediately.