3. Line a rectangular baking sheet with parchment paper and spread the cookie mixture evenly across the bottom of the pan. Press down firmly with the back of a spoon to compact the base. Refrigerate for 30 minutes to solidify the base.
4. Meanwhile, prepare the chocolate cream. Chop the dark chocolate and place it in a heatproof bowl.
5. In a saucepan, heat the whipping cream without boiling it. When condensation begins to form on the edges, pour it over the chopped chocolate. Let it sit for a few minutes, then mix gently until you obtain a smooth and homogeneous cream.
6. Add the icing sugar and cocoa powder to the chocolate cream and mix until well incorporated.
7. Pour the chocolate cream onto the biscuit base in the pan and level the surface with a spatula.
