Dip the mackerel fillets in seasoned flour and shake off the surplus. Melt the butter in a heavy frying pan until slightly frothing. Put in the fish fillets flesh side down, and cook gently for about 5 minutes. Turn and cook the second side. Lift on to a serving dish and keep warm.
Increase the heat under the pan until the butter turns a golden brown. Add the lemon juice and shake the p