Combine the milk, sugar, a pinch of salt and the flour. Add the egg yolks and melted butter. Mix well.
Leave the batter to rest in a cool place for 1 hour. Whisk the egg whites into peaks.
Add the grated parmesan and the beaten egg whites to the batter. Cook the batter for 3 to 5 minutes. Serve as an aperitif or with salad.