Whisk egg whites until they form soft peaks.
Gradually add sugar while whipping to make a firm meringue.
Add milk and flour to the egg yolks and mix well.
Gently fold the meringue into the yolk mixture in 2-3 batches.
Spread a little butter in a pan and pour in the batter.
Cover the pan and cook slowly over low heat.
Once the soufflé has risen, transfer it to a plate.