Pre-heat oven to 350 degrees Fahrenheit. Grease and line a ¼ sheet cake pan (9 x 13 inches or similar) with parchment and set aside
Whisk or sift together the flour, cocoa powder, baking powder, baking soda, and salt.
Using a hand mixer or large bowl and whisk, mix together the sugar and oil until smooth until some of the sugar begins to dissolve, about 2 minutes.
Add the eggs and the vanilla. Mix until combined.
Add half of the flour mixture and switch to a rubber spatula to mix to combine. Continue mixing while streaming in the buttermilk. Mix until smooth. Add the remaining flour mixture and mix until combined.
Slowly stream in the hot water and mix until the batter is smooth.
Pour the batter into the prepared pan and bake for 30 to 35 minutes, or until a toothpick inserted into the center of the cakes comes out clean or with a few moist crumbs.