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1
Position a rack in the middle of the oven and preheat oven to 300u00b0F.
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2
Butter and flour 9 inch spring form pan and line bottom with parchment paper.
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3
Melt the chocolate with the butter in a heatproof bowl set over a saucepan of about 1.5 inches of nearly simmering water, whisking until smooth.
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4
Remove bowl from heat and let cool to room temperature.
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5
Beat egg yolks and 3/4 cup of the sugar with an electric mixer on medium-high speed in a large deep bowl for 4 to 5 minutes, until very thick and pale.
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6
Beat egg whites with clean beaters in another large bowl just until the whites form soft peaks when the beaters are lifted. Beat in the remaining 1 tablespoon sugar.
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7
With a whisk or rubber spatua, gently fold in 1/3 of the cooled chocolate mixture into the egg yolk mixture. Then fold in 1/3 of the egg whites.
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8
Repeat, adding the chocolate and egg white mixtures alternately in thirds until all of the ingredients are combined.
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9
Transfer the batter to the prepared pan.
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10
Bake for about 30 minutes until the edges are firm and the centre is puffed but still a bit jiggly; do not overbake.
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11
Transfer to a wire rack to cool completely.
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12
To serve, remove sides of pan. Dust the cake with a layer of cocoa and then a layer of confectioners' sugar. Repeat with a second layer of cocoa and a final layer of sugar. Cut into thin wedges.
