In medium bowl, combine flour, baking soda and salt. In large microwavable bowl, melt chocolate and butter for 2 minutes or until butter is melted. (Mixture can also be melted on top of stove in heavy saucepan over low heat.) Stir until smooth. Transfer to large bowl; add sugar and beat with electric mixer until well blended. Add eggs, one at a time, and vanilla; mix well. Add flour mixture alternately with milk; beat until well blended and smooth. Pour into prepared pans.