Carefully place a bundt cake pan or round cake pan over medium heat with the sugar in it to melt the sugar for about 3 minutes (without touching the sugar at all) until a liquid caramel is formed, which should be evenly spread on all sides of the pan.
Remove from heat and set aside until needed.
For the flan (creme caramel):
Preheat the oven to 360º F (180° C). Place all ingredients in a blender or food processor and blend for 1-2 minutes until smooth.
Pour this mixture into the mold with the caramel and set aside again until needed.
For the chocolate cake:
In a medium bowl sift the flour with the cocoa powder and salt.
Crack open the eggs and place the egg whites in a large bowl and the yolks in different, medium bowl.
With an electric mixer or hand whisk, beat the egg whites for 1 minute until soft peaks begin to form. Add half of the sugar and continue beating for 2-3 minutes more until stiff peaks form.
With the same mixer, beat the egg yolks with the remaining sugar for 2-3 minutes until a light, slightly thick mixture forms.
Continue beating the egg yolks and in the meantime add little by little (in a trickle) the melted butter with the vanilla extract and the boiling water. Beat for 1 more minute until you have a smooth and homogeneous mixture.
Add the flour to the same bowl of yolks in three additions, beating for 30 seconds after each addition until everything is well integrated.
Using a rubber spatula, fold in the beaten egg whites in three additions, makingfolding motions very carefully as to not to deflate the batter.
Once the mixture is ready, pour it into the same bundt cake pan or round cake pan, on top of the flan and spread it evenly so that it covers the entire surface. Cover the pan with aluminum foil or cover the mold itself if it has one.
Place this cake pan in another high-walled rectangular mold with water to cook in a double boiler and place in the oven at 360º F (180° C) for approximately 45-55 minutes.
Once the chocoflan is ready, wait for it to cool down completely at room temperature and then refrigerate it for at least 5 hours or overnight.
Unmold the chocoflan in a dish as it will release liquid from the caramel, and it is ready.