Msr. Asfaux,
What is the traditional way of making this? I have been told it is many thin layers of chocolate mousse and chocolate genoise. Perhaps this is a modern interpretation?

Hi Douglas
You are right : some traditional chocolate marquise recipes include layers of chocolate stuffing and of biscuit but usually few layers.
Mr Asfaux's recipe is close to most other modern ones, i.e. without any biscuit.
'Marquise' refers to a chilled rectangular moulded dessert, without any systyematic reference to biscuit layer(s).