Preheat the oven to 350 degrees. Grease and flour (or grease and line with parchment rounds) two 9" round cake pans.

Whisk together the flour, cocoa, baking soda, baking powder, and espresso powder (if using).

In a large bowl or stand mixer, beat the eggs with the sugar and vanilla on high speed until very light and fluffy (at least 3 minutes).

Reduce the speed to low and add the mayonnaise, beating until well-combined.

Add the flour mixture and the water to the batter in three additions, alternating between the wet and dry. Mix until just combined. Don't overmix!

Divide the batter evenly between the two pans and bake for about 30 minutes, or until a tester inserted in the center comes out clean and the cake just begins to pull away from the sides of the pan.

Remove from the oven and let cool for 10 minutes in the pan before turning out onto a wire rack to cool.