First mix together the flour, sugar, baking soda, and cocoa in a large bowl. Then in a separate bowl, mix together the water, mayo, applesauce, vanilla, and apple cider vinegar. Once the wet in ingredients are mixed together well, add them to the dry ingredients and blend with a hand mixer for about 2 minutes, scraping the sides as you go.
Once the dry and wet ingredients have been well mixed, pour into a greased 9x13 cake pan. Bake in a preheated 350F oven for 25-30 minutes. When a toothpick poked in the center of the cake comes out dry, its done. Let the cake cool for 10-15 minutes before frosting.
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