Combine and mix well. Mix cornstarch, flour, and seasonings until well blended. Add beer and mix well. Cut about 3/4" off top of onion and peel. Cut into onion 12 to 16 vertical wedges, but do not cut through the bottom root end. Remove about 1" of petals from the center of the onion. You may want to separate the onion petals slightly, but do not do this too much or you will destroy the onion.
Dip onion in seasoned flour; remove excess by shaking. Separate petals to coat thoroughly with batter. Dip in the batter. Dip in flour mixture again. Gently place in fryer basket and deep-fry at 375 to 400 degrees for 1 and 1/2 minutes. Turn over and fry an additional 1 and 1/2 minutes. Drain on paper towels. Place onion upright in a shallow bowl and remove center core with circular cutter or apple corer. Serve hot with Creamy Chili Sauce.