Mix cornstarch, flour, and seasonings until well blended. Add beer, mix well.Cut about 3/4 inch off top of onion and peel. Cut into onion 12 to 16 vertical wedges, but do not cut through bottom root end. Remove about 1 inch of petals from center of onion.
Dip onion in seasoned flour and remove excess by shaking.
Separate petals and dip in batter to coat thoroughly.
Gently place in fryer basket and deep fry at 375 to 400 1 1/2 minutes. Turn over, and fry an additional 1 1/2 minutes.
Drain on paper towels.
Place onion upright in shallow bowl and remove center core with circular cutter or apple corer.