In lg bowl, combine flour, sugar, baking cocoa, baking soda, salt, 1 cup sour cream and egg. Beat w/ mixer until smooth. Heat oven to 350. Spray a 8"-square pan w/ cooking spray. Pour batter into pan. Bake 25 mins, or until a toothpick inserted in center comes out clean.
In bowl, combine 1 cup sour cream, powdered sugar and vanilla. Mix well. Fold in whipped topping.
When cake is cooled, frost w/ sour cream frosting.