Sift the flour and add the salt. Melt the dark chocolate and butter in a hot water bath; as soon as it begins to cool down, add the sugar and mix with an electric beater.
Add the vanilla extract and the eggs, one at a time. Carefully amalgamate all the ingredients, then add the flour and salt. Pour the batter into a square cake mold (21 cm x 21 cm) and level out the surface with a spoon.
Sprinkle with crushed hazelnuts and pistacchios di Bronte and bake in a pre-heated oven at 170°C for about 30 minutes.
The brownies are done when they have a thin crust and moist interior (test them with a toothpick before removing from the oven). Once you have taken them out of the oven, let them cool down still in the mold for a few minutes, then cut them into nine smaller squares and allow them to finish cooling on a rack.