Preheat oven to 350°F. Spray 13 x 9-inch pan with vegetable pan spray.
In small heavy saucepan or microwave safe bowl, melt butter and chocolate; stir until blended. In large bowl, combine chocolate mixture with sugar; mix well. Add eggs and vanilla; blend well. Combine flour and salt. Add to chocolate mixture; stir until all flour is mixed in. If desired, stir in nuts. Spoon into prepared pan.
Bake 40-45 minutes or until toothpick inserted in center comes out clean. Cool completely.
Makes about 32 brownies.