Preheat your oven to 350°F (175°C) and grease an 8-inch round cake pan. No parchment drama needed—just good old-fashioned grease.
In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, and salt. Take your time; lumps are the enemy.
Add in the water, vegetable oil, vinegar, and vanilla. Stir until everything looks smooth and slightly glossy. If it smells chocolatey, you're doing great.
Pour the batter into the prepared pan and smooth the top with a spatula. It’ll look thin—don’t panic, that’s normal.
Bake for 30 to 35 minutes or until a toothpick poked into the center comes out clean. No batter clingers allowed.
Let it cool in the pan for 10 minutes, then transfer to a wire rack. Slice once fully cool or devour warm—your call.