Separate the egg whites and yolks.
In a bowl, add the egg whites and sugar, then whip until stiff peaks form.
In another bowl, mix the egg yolks, milk, and cake flour to make a batter.
Fold the egg white meringue into the yolk batter evenly.
Heat a pan over low heat and add butter.
Pour the batter into the pan, cover with a lid, and cook for 5-7 minutes.
When the soufflé rises and puffs up, it's ready.