01 -
Preheat your oven to 350°F (175°C). Grease an 8×8 inch baking pan thoroughly, or line it with parchment paper for easier removal.
02 -
In a large mixing bowl, combine the all-purpose flour, sugar, cocoa powder, baking powder, and baking soda. Whisk or stir together until thoroughly mixed and no lumps remain.
03 -
To the same bowl with the dry ingredients, add the water, mayonnaise, milk, and vanilla extract. Using a wooden spoon or rubber spatula, stir everything together until just combined and you have a smooth batter. Don't overmix.
04 -
Pour the batter into your prepared 8×8 inch baking pan, spreading it evenly to the corners. Bake in the preheated oven for 40 minutes, or until a toothpick inserted into the center comes out clean or with just a few moist crumbs.
05 -
Remove the cake from the oven and place it on a wire cooling rack. Allow it to cool completely in the pan before frosting with your favorite frosting. If you try to frost the cake while it's still warm, the frosting will melt.
06 -
Once frosted, cut the cake into squares and serve. Store any leftovers in an airtight container at room temperature for up to 3 days, or in the refrigerator for longer storage.