Separate the egg yolks from the egg whites putting them in different bowls.

Beat the egg yolks with the sugar until the mixture is pale yellow, thick and forms a ribbon.

Incorporate the flour, little by little alterning with the milk (starting and finishing with the flour). Then add the butter and mix.

Beat the egg whites until soft peaks form, and incorporate them to the previous mixture  carefully with a rubber spatula. 

Pour a third of the mixture onto a hot pan with a little butter, that the mixture covers the whole surface, like it would happen with an omelette.

Wait 3 minutes just for the pancake to cook and then flip it. Tear the pancake irregulary with the spatula.

Then on top of that pour a third part of the brown sugar and keep moving so that the sugar starts to melt. 

Repeat the process from the 6th step twice more , until there´s no more mixture left and you are done!