Grease and flour 15 x 10 in. jelly roll pan.
Whisk together first 5 ingredients. Set aside.
Bring water to boil in medium saucepan. Remove from heat and add butter and shortening. Let stand until melted. Whisk together sour cream, vinegar, eggs, and vanilla. Whisk egg mixture into flour mixture until blended. Pour batter into prepared pan. Bake 400 for 18-20 minutes. Cool for 10 minutes and frost in pan while warm.
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