Peel and slice onions crosswise into 1 inch pieces. Place in cold water while preparing batter. Combine egg yolks and club soda. In separate bowl, sift together dry ingredients. Mix well into soda/egg mixture to make smooth batter. Whip egg white until peak forms and is fluffly. Fold into batter.
Heat one and a half to two inches of oil in a deep pan. (350F is ideal).
Dredge onions in flour then dip into batter. Fry in deep fat at 350 degrees.
Remove and drain excess fat, then salt to taste.
Enjoy with your favorite sauce!