01 - Preheat the oven to 350°F. Grease and flour two 8-inch round cake pans, ensuring thorough coverage to prevent sticking.
02 - Sift together flour, cocoa powder, baking powder, baking soda, and salt in a large bowl. This aerates the mixture and ensures even distribution of leavening agents.
03 - Whisk mayonnaise, granulated sugar, brown sugar, and vanilla extract in a separate bowl until completely smooth and creamy.
04 - Alternate adding dry ingredients and cold water to the mayonnaise mixture, beginning and ending with dry ingredients. Mix gently until just combined—avoid over-mixing to prevent tough texture.
05 - Divide batter evenly between the prepared pans, smoothing the tops with a spatula for uniform baking.
06 - Bake for 30 to 35 minutes until a wooden toothpick inserted into the center emerges clean or with only a few moist crumbs.
07 - Let cakes rest in pans for 10 minutes before carefully turning out onto wire racks. Allow to cool completely before frosting and decorating as desired.