PREHEAT oven to 350° F.
COMBINE cake flour, sugar, cocoa, baking soda and salt in ungreased 13 x 9-inch baking pan. Make 3 holes in mixture. Into the first hole, pour the vanilla extract, into the second hole, the vinegar and into the third hole, the vegetable oil. Pour cold water over all. Mix with fork or wire whisk until well blended; do not overbeat. Mixture may contain some small lumps.
BAKE for 35 to 40 minutes or until wooden pick inserted in center comes out clean. Cool completely in pan on wire rack. Dust with powdered sugar.