Beat the eggs and sugar well, until they become a smooth, creamy and fluffy mix. Add vanilla and beat some more.
Melt the grated chocolate with butter in a pan in a water bath, cool the mixture and add it to the egg whites, while beating continuously and slowly. Using a spatula, mix in the sifted flour with the salt to the blend.
Do not mix too much, finally add the chopped walnuts. Pour the mixture into a rectangular oven dish, greased and covered with baking paper. Put it in a preheated oven at 356°F (180 °C) for 25 minutes.
The top needs to have a slightly lighter crust and the inside has to remain moist and soft. Sprinkle walnuts over the brownies and set aside to cool. Remove the paper and cut them into squares.