1Preheat oven to 350 degrees Fahrenheit.
2Break the eggs into a bowl, whisk them well, and set aside.
3In a saucepan, heat the sugar and water over medium heat, whisking to dissolve the sugar.
4When the sugar is dissolved, bring to a boil, and then immediately remove from heat.
5Add the chopped chocolate pieces and stir until completely melted.
6Then, add the diced butter and stir to incorporate into the above mixture.
7Wait 5 minutes before adding the beaten eggs.
8Sprinkle flour over the chocolate batter and stir in with a whisk.
9Pour the batter into the pan and bake for 30 minutes.
10Gently shake the pan to make sure the center of the cake does not move, if it doesn't move the cake is done.
11Remove the cake from the oven and let it cool for about 5 minutes on a raised rack before unmolding it on a plate.
12Wrap the cake in plastic wrap and put it in the refrigerator until serving time.
13The cake is best very cold.
14Sift cocoa powder on top of it just before serving.