Sift together flour, baking soda, sugar, salt, and cocoa. Place the sifted ingredients in a square cake pan. Make three holes in the mixture, and into each hold put in the following: Vinegar, Vanilla, and butter.
Pour 1 cup cold water over top and mix well. Bake in a 350-degree oven for 30 minutes or until toothpick comes out clean. This is good served warm with ice cream.