1. Preheat the oven to 400' F (205' C). Bring a pan of water barely to a simmer. Place the chocolate and butter in a double boiler or metal mixing bowl and place over the pan of hot but not simmering water. Heat, stirring occasionally, until the mixture has melted but is not too hot. Stir until smooth.
2. In a mixing bowl, whisk the egg yolks and four-sevenths [1/4 cup/60ml] of the sugar together until thickened slightly and lighter in color. Whisk in the flour and then the chocolate mixture.
3. Place the egg whites in a metal bowl and place over hot water until warmed slightly. Add 1 tablespoon (15 ml) of sugar and whip with an electric mixer on medium-low speed until soft peaks form. Gradually add 1 1/2 tablespoons (21 ml) more sugar. Turn the speed to high and add the remaining sugar, whipping the whites to firm peaks.
4. Stir a third of the egg whites into the chocolate mixture. Fold in the remaining whites. Divide the batter among 6-ounce tins. (The recipe can be made to this point up to 1 1/2 hours before serving; refrigerate.)
5. Place the tins on a baking sheet and bake until the tops are puffed and feel firm to the touch but are very liquidy in the center, about 8 minutes (or a few minutes longer if they were cold).
6. Meanwhile, sift a little cocoa lightly over dessert plates. Three minutes after the cakes are done, run the tip of a knife around the sides to loosen, and unmold the cakes onto the plates, rinsing the knife with hot water between each one. Serve immediately.
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