Preheat the grill to high.
Place the béchamel sauce, fresh chives, double cream, egg yolk, salt and freshly ground black pepper into a bowl and mix together well.
Add the egg whites and fold into the mixture gently to maintain volume.
Melt the butter in a small ovenproof frying pan and when foaming pour in the egg mixture.
Sprinkle over the crab cook for 3-4 minutes, or until the base has set.
Transfer to the grill and cook for 2-3 minutes, or until browned and set but still slightly wobbly in the middle.
To serve, slide the soufflé onto a plate and sprinkle over the spring onions.