In a bowl, whisk flour, sugar, cocoa, baking soda and salt together. Make 3 wells in mixture.
Add vanilla, oil and vinegar to each of the wells. Pour in cold water and whisk together until no lumps are left.
Pour into an ungreased 9×13 baking pan. Bake for 25-30 minutes or until a toothpick comes out clean. Let cool before cutting. Dust with powdered sugar or top with frosting.