Melt the chocolate and butter in a bain-marie. Pour the mixture into a bowl and add the sugar, flour, eggs and finely crushed hazelnuts or walnuts.
Mix well. Pour the mixture into a buttered and floured mold. Cook for around 30 mins at Th. 4°.
Unmold and cut into small square pieces. Do not make too large portions because the brownie is very "rich"!