3 c. flour
1 1/2 c. sugar
1/3 c. cocoa
2 1/4 tsp. baking powder
1 1/2 tsp. baking soda
1 1/2 c. mayonnaise
1 1/2 c. water
1 1/2 tsp. vanilla

Sift together dry ingredients into large bowl. Stir in mayonnaise. Gradually stir in water and vanilla until smooth and blended. Pour into 13x9x2 pan. Bake at 350 degrees for 40 minutes.