Wash the spinach thoroughly, then cook without added water in a large, non stick saucepan until soft. Drain, squeeze dry and chop finely. Fry the onions in the oil and butter until soft.

Chop the anchovies finely and add to the pan with the spinach.

Fry for 1 minute, then puree in a blender with the chicken stock until smooth.

Season with freshly ground black pepper.