Butter 6 ramekins really well and refrigerate.
Melt butter, add flour, make a roux and add hot milk gradually, whisking to keep it smooth. Add egg yolks and cheese and season with salt and pepper.
Whisk the egg whites until stiff and add the chives. Add the crab to the cheese mixture, gently fold in half of the egg whites, then fold in the rest.
Fill ramekins to the top,