Sweat the onion in a large casserole dish with a drizzle of oil and a pinch of salt. Once golden add the finely chopped fennel and keep cooking on a low heat for about 8 minutes until the fennel becomes soft. Blend well, pass through a fine sieve and season to taste. Keep the fennel purée aside.
Drain the anchovy fillets and cut them into strips.
In a large pan fry the garlic wi