Mayonnaise Chocolate Cake

1 c. sugar
1 c. water
1 egg
2 c. flour
1 c. mayonnaise
2 tsp. baking soda
1 tsp. vanilla
5 tbsp. baking cocoa

Cream sugar and mayonnaise. Add egg and vanilla. Dissolve baking soda in water and add to first mixture. Sift flour and cocoa together and stir into mixture. Pour into a greased 13x9x2-in. baking dish and bake at 350 degrees for 30 minutes.