Preheat the oven to 180 degrees. Grease a baking pan (20 cm) with a little butter.
Melt the butter over medium heat. Either grate the chocolate or chop it into small pieces. When the butter has melted, remove the pan from the oven and add the chocolate. Let stand a few minutes until the chocolate has melted, then stir.
Put the eggs and vanilla in a large bowl and beat with the kitchen utensil or mixer until the mixture is nice and airy. Add the sugar in two installments so that the mass is not killed. Keep mixing in between until the mixture has become a little stiffer.
Add the liquid chocolate, flour, cocoa powder and salt, ideally placing everything in the side of the bowl so that the egg mixture does not collapse. Fold in everything, do not mix any more. Crumble a third of the biscuits and add to the mixture, fold in briefly.
Put the finished mixture in the baking pan and crumble the rest of the biscuits over it. Press the biscuit pieces lightly into the dough.
Bake on the middle rack for 25-30 minutes. The brownies should still be a bit sticky in the middle. Allow to cool in the mold. Cut into small rectangular pieces and dust with powdered sugar if you like.