Preheat oven to 325 degrees.
Grease a 9 inch springform pan
Line bottom with parchment paper, and butter the paper.
Melt chocoalte and butter. Cool slightly.
Beat eggs with an electric mixer until they are pale and double in size. Gradually beat in the sugar. Fold in the chocolate into the egg mixture until the batter is smooth and uniform in color.
Pour batter into pan, smooth the top with a rubber spatula. (I don't actually do this). Bake for 25 minutes or until 1 to 2 inches around the edges start to firm. The cake should be soft and creamy in the middle.
Transfer to a wire rack to cool for 20 minutes. Run a long metal spatula around the edges of the cake to loosen it from the pan (I use a knife). Open the spring, and let the cake cool completely.
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