Sift the flour, sugar, cocoa, baking soda, and salt together into a mixing bowl. Make 3 wells in the dry ingredients. Pour vanilla into 1 well; vinegar into 1 well and melted butter into the third. Pour water over all. Beat with a wooden spoon until well blended. Pour batter into a greased 23 cm square baking pan. Bake in a preheated 180ºC . oven for 25 minutes or until cake tests done. Cool in pan on rack. Frost with Mocha Chocolate Frosting. Cut into squares. MOCHA CHOCOLATE FROSTING: Combine confectioners' sugar, cocoa, softened butter, coffee, and vanilla in a mixing bowl. Beat, with an electric mixer set at medium speed, until smooth. NOTE; This recipe came from a very old church cookbook that the woman found and is typical of many of the recipes of the 1800's. The vinegar was used to keep the cake from spoiling. Try this and I think that you will like it.