Remove the skin and seeds from the pumpkin and steam it.
Mash the steamed pumpkin until smooth.
Melt the dark chocolate in a double boiler.
Add eggs and sugar to a bowl and whisk together.
Add the mashed pumpkin, melted chocolate, and butter, and mix well.
Sift cake flour and cocoa powder into the mixture and fold gently.
Pour the batter into a mold and bake in a 170°C oven for 25 minutes.
Let it cool, then cut into slices to serve.