Clean, sour and salt the fish fillets. Cover the smooth side of the skin with slices of ham and cheese, fold over and pin in place with toothpicks. Turn in flour, beaten egg and breadcrumbs.
Fry in hot oil over medium heat until golden brown. Put a flake of butter on each piece of fish, cover the pan and let the fish simmer for 5 minutes.
Cut the lemon into slices. Spread the fish on warmed plates, decorate with a lemon wedge and add some caviar on top.