Place a handful of flour on a plate, season with salt and pepper and coat the fish in it, shaking off any excess. Give the batter a stir, dip the fish in it, allowing any excess to drip off, then fry for 3–5 minutes (depending on the thickness of the fish), until the batter is dark golden and crisp. Lift out with a slotted spoon, drain on kitchen paper and season with a pinch of salt. Keep warm while you cook the remaining fish in the same way.