Mix the 100ml buttermilk, cumin and a large pinch of salt together in a bowl. Put the quail halves in the buttermilk mix so they are completely covered, then chill for at least 6 hrs or overnight.
To make the dressing, beat the mayonnaise, buttermilk, cheese and celery salt together – don’t worry if it’s not totally smooth. Keep chilled.
When ready to cook, mix all the spiced flour ingredients together. Heat a deep-fat fryer or a deep pan with sunflower oil to 175C. Remove the quail from the fridge, then dip each half in the spiced our and carefully drop them in the fryer.
Fry for about 6 mins until golden and crisp, then drain on kitchen paper and leave to rest for 2 mins or so. Pile onto a large serving plate, put the blue cheese sauce on the side for dipping, and scatter over the celery leaves, if you like.