Preheat oven to 325°F. Spray pan with vegetable pan spray.
In large bowl, beat butter and sugar with electric mixer until light and fluffy. Add eggs, chocolate and vanilla; mix well. Combine flour and salt; stir baking soda into sour cream.
Alternately add sour cream and flour mixture to butter mixture. Pour batter into prepared pan.
Cool 10 minutes in pan on rack; remove and cool completely before decorating.
Refer to baking chart in techniques section for baking times and temperatures for specific pans.
YIELD: Makes about 6 1/3 cups batter.