Preheat the oven to 190 C / Gas 5. Put a baking sheet in the oven. You will also need 3 ramekins- greased.
Melt the butter in the saucepan, then add the flour and cook for 1 minute.
Slowly add the milk, stirring all the time, to make a smooth, thick sauce. Take off the heat and allow to cool slightly.
Add the grated cheese and egg yolks to the milk sauce.
Whip the egg whites to soft peaks, stir one spoonful into the cheese and yolk mixture.
Use a metal spoon to stir the cheese sauce mix into the rest of the egg whites. Split this into the 3 ramekins.
Place on the baking tray and bake in the oven until the souffle has risen and is golden on top, 15 to 20 minutes. Serve immediately as it will quickly sink in cool air.
Other ideas
It's your choice if you want to use 2 tablespoons chives, or a pinch of cayenne pepper and a pinch of mustard powder.