Preheat oven to 350°F and prepare an 8-inch square pan with butter or non-stick baking spray.
Add the flour, cocoa powder, sugar, baking soda, and salt directly to the greased pan and carefully whisk to combine.
Use a spoon to scoop out one large well or indention in the middle of the dry ingredients, as well as two small wells against the sides of the pan.
Pour the vinegar and vanilla into the small wells on the sides and pour the oil in the big well. It's ok if the liquid ingredients spill over onto the rest of the cake.
Pour the water over the top of the cake and whisk again to combine everything thoroughly.
Bake for 30-35 minutes or until a toothpick inserted in the center of the cake comes out clean.
Cool completely and frost with your favorite chocolate frosting.
Note: Nutrition information is a rough estimate only; actual values will vary based on the exact ingredients used and amount of recipe prepared. Nutrition info above does not include any additional frosting.