1. Preheat oven to 325 degrees F. Butter, flour and line the base of a 10-inch round cake pan with parchment.
2. Combine chocolate and butter in a bain marie or in a bowl over simmering water.
3. Whisk together the egg yolks and all but 3 tablespoons of the sugar. Stir melted chocolate into egg yolks until thoroughly combined.
4. With an electric mixer, on medium speed, beat egg whites and salt until soft peaks form.
5. Gradually beat in the remaining sugar and continue to whip until egg whites are stiff but not dry.
6. Carefully fold chocolate mixture into egg whites. Pour into prepared pan.
7. Bake for about 45 minutes.
8. Turn out onto a rack immediately.
9. As the cake cools, the center will sink and crack - do not worry.

Yield: 12 servings