Prepare four small soufflé dishes by greasing well with butter. Add a little flour to each and swirl to coat the base and the sides. Place the prepared dishes into the fridge to chill.
Preheat the oven to 180c(fan)/200c/Gas Mark 5.
Melt the Stork in a pan. Add the plain flour and mix well. Add the milk a little at a time, whisking well. Continue adding and whisking until all the milk is incorporated and the mixture is smooth.
Cook for ten minutes over a low heat whisking continuously.
Remove from the heat and stir in the finely grated gruyere.
Beat in the egg yolks and set the mixture to one side.
In a clean grease free bowl whisk the egg whites until they are thick and creamy and stand in stiff peaks.
Take 1/3rd of the egg whites and beat quickly into the cheese mixture. This loosens the mixture and makes folding the in the remaining egg whites much easier.
Add the remaining 2/3rd of the egg whites to the cheese mixture and fold in gently and carefully using a palette knife. Lift and turn the mixture to incorporate the egg whites taking care to retain the lightness of the whites. Once combined the mixture should be airy and light.
Fill each of the soufflé dishes to the very top with mixture and level.
Run the tip of your finger around the inside edge of the dish to create a groove in the mixture allowing the soufflé to rise upwards when baked.
Bake in the oven for 18-20 minutes until well risen and golden.
Why not use Parmesan or your favourite hard cheese instead of Gruyere?
A lightness of touch is needed when folding in the egg whites, if too much air is knocked out at this stage your soufflé will not rise when baked.