Chocolate Mayonnaise Cake

Why I Love This Recipe
I'm not sure where I originally found this recipe. It's been in my cookbook for decades. I really like it because it makes a small cake, and the ingredients are items I usually have on hand. It's a VERY moist cake and it's delicious!
Ingredients You'll Need
2 cups flour
1 cup sugar
1/2 cup cocoa
1-1/2 teaspoons baking powder
1 teaspoon baking soda
1 cup mayonnaise (don't use light mayonnaise)
1 cup water
1 teaspoon vanilla.
Directions
Preheat oven to 350°. Grease and flour a 9" x 9" x 2" baking pan.
Mix flour, sugar, cocoa, baking powder and baking soda. Stir in mayonnaise. Gradually stir in water and vanilla until smooth and blended. Pour into prepared pan. Bake at 350° for 40-45 minutes. Cool.