Have all ingredients at room temperature.
Preheat oven to 350°F and place oven rack in the center of the oven.
Spray the pan with a non-stick vegetable spray then flour it, or line the bottom of the pan with parchment paper and spray it.
In a large bowl whisk or sift together the sugar, flour, cocoa powder, baking powder, baking soda, and salt.
In another bowl, whisk together the eggs, water (and/or coffee), milk, oil, and vanilla extract.
Add the wet ingredients to the dry ingredients and stir or whisk until combined (the batter will be quite thin).
Pour the batter into the prepared pan and bake for 20 - 30 minutes or until the cake starts to pull away from the sides of the pan, it springs back when you lightly tap the middle of the cake, and a toothpick stuck in the middle comes out clean. Do not under-bake.
Remove from the oven and let cool on a wire rack for about 10 minutes, then turn the cake out of the pan.
Serve warm or at room temperature plain or with whatever toppings you like.
Be sure to let the cake cool completely before frosting.