Heat the butter in a saucepan, add the onion and fry gently for 5 minutes until just beginning to soften. Stir in the broccoli until coated in the butter then add the ground almonds, stock and a little salt and pepper.
Bring to the boil then cover and simmer for 10 minutes until the broccoli is just tender and still bright green. Leave to cool slightly, then purée in batches in a blender or food processor until finely speckled with green.
Pour the purée back into the saucepan and stir in the milk. Reheat then taste and adjust the seasoning if needed. Heat the 15 g (½ oz) butter in a frying pan, add the almonds and fry for a few minutes, stirring until golden. Ladle the soup into bowls, drizzle a spoonful of yogurt over each bowl, then sprinkle with almonds.