Heat the olive oil in a saucepan, add the onion and fry for 2-3 minutes, or until softened but not coloured. Add the garlic and fry for a further minute.
Stir in half of the spinach and leave to wilt in the pan for 1-2 minutes, then add the chicken stock, milk and butter and simmer for 5-6 minutes. Stir in the remaining spinach, season well with salt and freshly ground black pepper and cook for a further minute until the spinach is wilted.
Using a stick blender, blend the soup until smooth.
To serve, ladle the soup into a serving bowl, top with the poached egg and drizzle over a little olive oil.
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