Microwave butter and chocolate, stir until smooth
In a large bowl, beat sugar and eggs
Stir in vanilla and chocolate mixture
Combine flour and salt; gradually add to chocolate mixture
Sir in pecans if desired
Spread into two greased 8-in square baking pans.
Bake at 325 for 35-40 min or until a toothpick inserted near the center comes out clean.
Cool on a wire rack and dust with confectioners' sugar if desired.
Cut into bars.