1 Heat the butter and fry the onion until golden. Dust with icing sugar and cook until caramelised and golden brown. Spread out on aluminium foil to cool.
2 Halve the melon, remove the seeds and cut into wedges. Peel and roughly chop the flesh. Put into a liquidiser with the buttermilk, sugar and crushed ice and puree very finely.
3 Pour into 4 bowls and serve garnished with lavender and caramelised onions.