Sift dry ingredients into an 8" square or 9" round baking pan. Mix liquids except the vinegar and wisk into dry ingredients. When the batter is smooth, add the vinegar and stir quickly, until it is evenly distributed.
Gluten: Gluten is a protein found in specific grains (wheat, spelt, kamut, barley, rye). Other grains are naturally gluten-free but may have cross-contact with gluten-containing grains. Look for certified gluten-free products if you need to avoid gluten. Find out more about wheat and gluten substitutions.