Here's a recipe for "The Ultimate Onion" from The Vidalia Sweet Onion Lover's Cookbook (published by Bland Farms here in Vidalia)

3 cups cornstarch
1-1/2 cups flour
2 tsp. garlic salt
2 tsp. paprika
1 tsp. salt
1 tsp. pepper
24 ounces beer
4 to 6 large Vidalia Sweet Onions (4" in diameter or larger)
Seasoned flour (made up of 2 cups flour, 4 tsp. paprika, 2 tsp. garlic powder, 1/2 tsp. pepper and 1/4 tsp. cayenne pepper)

Mix cornstarch, flour, and seasonings until well blended.
Add beer. Mix well.
Cut about 3/4 inch off top of onion, peel onion, cut onion into 12 to 16 vertical wedges, but don't cut through bottom. Remove about 1 inch of petals from center of onion. Dip onion in seasoned flour and remove excess by shaking, dip in batter and remove excess by gently shaking.Separate petals to coat thoroughly with batter. Mix batter after standing to blend ingredients. Gently place onion in fryer basket and deep fry at 375 degrees to 400 degrees for 1-1/2 minutes. Turn over and fry 1 to 1-1/2 minutes longer or until golden brown.
From National Onion Association

Serve with creamy chili sauce:
combine: 1 pint mayonnaise, 1 pint sour cream, 1/2 cup chili sauce, 1/2 tsp. cayenne pepper

watch the temperature of the oil--batter will fall off if the oil isn't hot enough.
enjoy!