Preheat oven to 350 degrees.
In an UNGREASED 8x8 pan add the flour, sugar, cocoa, baking soda, and salt. Using a whisk stir together the ingredients right in the pan to kind of sift it all together.
Next using your fingers or a spoon make a good sized well in the middle and two smaller wells one on each side of the center well.
Place the vegetable oil in the center well.
Place the vinegar in a small well and the vanilla in the other small well.
Pour the cold water over all of the ingredients.
Using the whisk, stir until combined. You can also use a spoon to get into the corners and further mix until smooth. If there are bubbles in your batter, gently tap the pan on the countertop to release the bubbles.
Bake for 30 to 35 minutes or until cake tester comes out clean. Remove from oven to cool completely before serving.
Ice with frosting or powdered sugar or plain.