2 c. flour
1 c. sugar
4 heaping tbsp. Hershey's cocoa
2 tsp. baking soda
1 tsp. salt
1 c. water
1 c. mayonnaise
1 tsp. vanilla

Mix dry ingredients in a large bowl. Add water, mayonnaise and vanilla. Mix for 2 minutes on medium speed. Pour in 9 x 9 square, lightly greased baking pan. Bake at 350 degrees for 30 minutes. Frost with buttercream frosting.