Onion soufflé

Preheat the oven to 180 ºC (354 ºF). Prepare a 1,5 litre soufflé dish.
Sauté onion in 15 ml butter until soft. Remove to a side dish.
Melt 50 ml butter in the pan and add the cake flour. Remove from the heat and stir until a smooth paste is formed.
Cook for one minute, stirring continuously. Remove from the heat and cool slightly.
Blend the cream and milk and slowly add to the mixture, stirring continuously.
Return to the heat and boil thoroughly. Season to taste and cool slightly in a glass bowl.
Beat the egg yolks into the mixture, one by one.
Add the onion and mix well.
Beat the egg whites until stiff peaks are formed and fold into the white sauce.
Turn the soufflé mixture into the prepared soufflé dish.
Run your finger round the inner edge of the dish to allow the soufflé to puff out into a crown.
Place on an oven rack in the centre of the oven and bake for about 35 minutes or until the point of a knife comes out clean when inserted into the centre of the soufflé.