Heat the olive oil in a saucepan and gently fry the onion and garlic until soft.
Add the chopped fennel and stock and bring to the boil. Reduce the heat and simmer for 12-15 minutes, or until the fennel is tender.
Add the spinach to the pan and season with salt and freshly ground black pepper. Cook for a further minute, then process with a hand-held blender until smooth.
To serve, pour into a bowl and garnish with yoghurt and a sprinkling of chopped chives.
