Put the eggs in a pan of just simmering water and cook for 10 mins. Turn off the heat, and leave the eggs to rest in the hot water for 2 mins. Drain, then transfer the eggs to a bowl of ice-cold water and leave to cool. Peel the eggs and slice in half, then scoop the yolks out into a bowl with the mayonnaise, yogurt, mustard, spring onions, celery salt and cayenne pepper. Mash everything together until smooth, then spoon into a piping bag fitted with a plain round nozzle.

Pipe the mixture into the hollowed-out eggs, or carefully spoon into the middles using a small spoon. Sprinkle over some chives, if using, then serve.