Grease an 8 inch round cake pan and line bottom with parchment paper. Grease the parchment paper.
In a double boiler or in a bowl in the microwave, melt chocolate and butter together.
Separate eggs. Remove chocolate from heat and stir in sugar, egg yolks and vanilla.
In a mixing bowl, beat egg whites until fluffy and a soft peak forms. Fold egg white mixture gently into chocolate mixture.
Pour into prepared pan. Bake for 30-35 minutes. Allow to cool in pan for 10 minutes. Remove from pan and allow to cool completely on a wire rack. Serve warm or chilled.
Before serving, remove from refrigerator and allow it to set at room temperature for 5-10 minutes. Dust with powdered sugar and top with berries and serve.