Break the chocolate in small pieces and melt it a bain-marie (place it into a bowl suspended over a saucepan of simmering water, stir occasionally) until smooth, shiny and glossy. While the chocolate is melting, break the biscuits in small pieces. Do it by hand, a machine would break them too much.
In another big bowl mix the soft butter and sugar, add the eggs one by one. When they are mixed very well, pour in the melted chocolate and stir.
Then add the broken biscuits and mix. Spread a baking paper and pour the mixture on, roll it up in a salame shape closing the ends. Roll it again in an aluminum foil, let it rest in the fridge for al least 4 hour.