Here's how to make a rich chocolate cake without butter, cream, or sugar. Sift together cocoa powder and cinnamon powder, then mix with milk to make the cocoa batter. Gradually add 3 whole eggs, mixing until smooth. Mix together melted couverture chocolate and rice oil in a double boiler, then add to the cocoa batter and mix until smooth. Strain the batter to remove air bubbles and pour into the prepared mold. Place the mold in a 70°C water bath and bake in a preheated oven at 170°C for 20-25 minutes. Once baked, let it cool slightly, then refrigerate overnight. It has a sticky, melt-in-your-mouth texture, and you can enjoy an even more melt-in-your-mouth texture by letting it sit at room temperature for about 20 minutes.