Preheat oven to 350 degrees. Mix the flour, sugar, baking soda, cocoa powder, and salt in a greased 8" square (or round...I prefer the round, but I've made this in both) baking pan.

Make 3 depressions in the dry ingredients - two small and one large. Pour the vinegar and vanilla in each of the two smaller depressions, and the vegetable oil in the large one.

Pour water over the entire thing and mix until smooth.

Bake on the middle rack of the oven at 350 degrees for 35 minutes. Let it cool, then top with your favorite frosting and enjoy!