Prepare all the ingredients.
Break the chocolate in pieces...
...and place in a saucepan with butter.
Melt on very low heat...
...until you obtain a very smooth mixture.
Crush the pistachios.
the eggs with sugar and a pinch salt.
Add vanilla, chocolate.
Mix...
...then add flour.
Mix.
And finally add the crushed pistachios. Mix.
Pour this batter in a square mold of 22 cm sides.
Bake in hot oven at 170°C for 25 minutes.
Check the cake by inserting the blade of a knife. If it comes out dry, the cake is ready.
When finished, leave to cool before cutting into pieces.