Preheat your oven to 375°F and lightly grease an 8-inch round baking pan. Place a round piece of wax paper at the bottom and grease it as well.

Chop the chocolate into small pieces. Melt the chocolate with the butter in a double boiler or a metal bowl over a saucepan with barely simmering water, stirring constantly until smooth. Remove the bowl or top of the double boiler from the heat and whisk in the sugar until it is fully combined with the chocolate.

Add the eggs and whisk until well mixed. Sift ½ cup of cocoa powder over the chocolate mixture and whisk until the cocoa is fully incorporated and the mixture is smooth. Pour the batter into the prepared baking pan and bake in the center of the oven for 25 minutes, or until a thin crust forms on the cake's surface.

After the cake is baked, take it out of the oven and let it cool in the pan on a wire rack for 5 minutes. Then, carefully invert the cake onto a serving plate.