I cut the onion into 16ths and soaked in ice water for about an hour to help open the onion up. Some guys core out the center , that's to put dip in if you want .
Allow it to dry and then into a seasoned flour dredge ( I used Italian seasoning, garlic and onion powder , cayenne , white pepper and black pepper. Spread the petals apart and get it coated well. Add 1 1/2 tsps of baking powder and 1/2 of salt to each cup of flour , this makes self rising flour and a fluffy crust.
Next dip into egg and milk mixture 1egg to 1 table spoon milk and then back into flour again. Now place in fridge for at least 30 minutes or longer if you have time , this helps set the egg on the onion.
After well chilled remove and roll into egg mixture again and then into a bag of seasoned bread crumbs , panko or whatever you like, spray with cooking spray and it's ready to grill . I cooked mine at about 300 for an hour on
in-direct heat, I basted with unsalted butter half way through the cook time . This temp will create a crispy crust and slow cook the onion to a nice tenderness, the petals should pull out with a slight tug . I used a cast iron pan but they can grill directly if you choose.