1. Preheat oven to 350F.

2. Stir together the flour and salt and set aside.

3. In a microwave proof bowl melt the butter and chocolate on low heat, stirring everything 20 seconds until just melted. Once it is melted add 1 cup of the sugar to the chocolate and stir well. Then stir in the vanilla. Pour the mixture into a large bowl.

4. In a small bowl whisk together the remaining sugar and eggs. Pour half of this mixture into the chocolate and stir well. With the remaining sugar and eggs whip until thick, pale, and doubled in volume.

5. Carefully fold the whipped egg mixture into the chocolate mixture, only stopping once it is just combined. Then carefully fold in the dry ingredients.

6. Pour the batter into a 9-inch square pan that has been lightly buttered. Bake for 25-28 minutes or until a cake tester comes out with only a few moist crumbs attach.