Melt butter. Mix flour, salt, baking powder, sugar and vanilla sugar.

Separate the yolks from the whites. Add egg yolks, milk, vanilla extract and melted butter to the dry mixture. Mix well to prevent lumps.

Beat the egg whites until firm. Delicately fold the egg whites into the mixture. Let rest for 2 hours at room temperature.

Paint the waffle iron with melted butter and heat it up. Pour mix onto hot waffle iron. Cook until golden brown. Serve hot.

You can prepare a batch in advance and freeze your waffles for later use. Remember to let the waffles cool down on a cooling rack. It is important to use a cooling rack so that the moisture can escape. If you were to place them on a plate, for example, the steam created by the cooking process would render your waffle "wet" and mushy.

Once your waffles are completely cold, place them in a freezing bag and remove as much air as you can from the bag. Place the bag in the freezer. Reheat your waffles in a toaster as you need them. You can keep them for up to a month in your freezer.