Heat a large frying pan. Season the flour on a plate. Lightly beat the eggs in a shallow dish with a pinch of salt and put the breadcrumbs in a separate shallow dish. Lightly dust the whiting fillets in the seasoned flour and then dip in the beaten egg, shaking off any excess. Coat in the breadcrumbs.
Add the olive oil and butter to the frying pan and cook the coated whiting fillets for 2-3 minutes on each side until crisp and golden brown. The exact time will depend on the thickness of the fillets.
Meanwhile, mix the mayonnaise with the dill and season to taste. Arrange the crispy whiting on warmed plates with the dill mayonnaise and some garden peas to serve.