In a saucepan melt the butter, add the flour and cook out for a few minutes. Gradually add the milk stirring constantly until thickened. Melt through the cheese and add the chives.
Remove from the heat and whisk through the egg yolks.
In a clean mixing bowl, use an electric whisk and beat the egg whites until soft peaks that hold their shape.
Add the egg whites to the cheese sauce mixture a spoon at a time, be careful not to over mix -knocking the air out, use a light folding action.