Heat oven to 350°F. Spray 13x9-inch pan with cooking spray. In large bowl, mix flour, sugar, baking soda and salt. In medium bowl, beat eggs. Gradually add melted chocolate, oil and vanilla, stirring with whisk until blended. Add chocolate mixture to flour mixture, stirring with whisk until blended. Stir in sour cream; mix well. Stir in beets and carrots. Pour batter into pan.