Bring a small pan of water to a boil over medium heat. Put a larger glass bowl on top. Break up the Dark Chocolate (0.5 pound) into smaller pieces. Chop up the Butter (0.5 pound). Add both chocolate and butter to the glass bowl and let them melt over the boiling water.
Stir well until you get a glossy chocolate mix. Pour in the strong Espresso (1/2 cup) and the Brown Sugar (3.5 ounce).
Mix well again and take the glass bowl off the heat. Let it cool down for 5 minutes.
Crack the Egg (4) and add them to the chocolate mixture.
Stir firmly until you get a silky but airy batte. Line a 6-inch (15 cm) diameter cake springform with baking paper. Pour in the chocolate batter.
Put the springform in another larger tray and fill it with water.
Put the tray in a preheated oven at 350 degrees F (180 degrees C) for 40 minutes.
Turn off the heat in the end but leave the cake in the hot oven for another 20 minutes. Remove it and let the cake cool down fully in the springform.
Chill the cake in the fridge overnight to set. Take it out of the springform. Carefully peel away the baking paper. Cut the cake into wedges and serve. Enjoy!