In an ungreased 8"x8" baking dish, add the flour, baking soda, salt, and sugar, and cocoa powder. Whisk together.
Make 3 small wells in the mix. Add the oil to one, vinegar to another, and vanilla to the third.
Pour the coffee (or water) over and gently whisk together just until combined.
Bake at 350° F for 30 minutes, or until a toothpick inserted into the center comes out clean. Be careful not to over bake.
Remove from oven and let cool in dish on a wire rack.
Frost if desired (the original had no frosting, but we like 1-Minute Chocolate Frosting Cut into 9 squares and serve.