Prepare the seasoned flour by combining the all-purpose flour, paprika, garlic powder, ground black pepper, and cayenne pepper in a mixing bowl.
Stir the seasoned flour mixture until the spices are evenly distributed.
Prepare the dipping sauce by combining the mayonnaise, ketchup, creamed horseradish, paprika, salt, dried oregano, ground black pepper, and cayenne pepper in a small bowl.
Mix the sauce thoroughly until smooth and fully combined.
Cover the sauce and refrigerate it for at least 2 hours, or overnight if time allows.
Prepare the batter by combining the cornstarch, all-purpose flour, minced garlic, paprika, salt, and ground black pepper in a large mixing bowl.
Add the beer to the dry batter ingredients.
Whisk until the batter is smooth and evenly blended.
Cut approximately 3/4 inch from the top of each Vidalia onion.
Peel each onion completely, leaving the root end intact.
Place each onion cut-side down on a stable cutting board.
Carefully cut each onion into 12 to 16 vertical wedges, stopping before reaching the root end.
Do not cut through the root end, as it is necessary to hold the onion together and create the bloom shape.
Gently separate the onion petals with your fingers.
Remove approximately 1 inch of the center petals, if needed, to help the onion open more fully.
If desired, place the cut onions in cold water for a few hours to help the petals separate.
If the onions are soaked, drain them thoroughly and pat them completely dry before coating.
Dip each prepared onion into the seasoned flour mixture.
Gently separate the petals while coating to ensure the flour reaches between the layers.
Shake off any excess seasoned flour.
Dip each floured onion into the prepared beer batter.
Carefully separate the petals as needed so the batter coats the onion evenly.
Heat oil in a deep fryer or deep pot to 375°F to 400°F.
Carefully lower one coated onion into the hot oil.
Fry for approximately 1 1/2 minutes.
Carefully turn the onion over.
Continue frying for another 1 1/2 minutes, or until the onion is crisp and golden brown.
Remove the fried onion carefully from the oil.
Transfer the onion to a paper towel-lined plate or rack to drain.
Repeat the frying process with the remaining onions, if preparing more than one.
Serve warm with the prepared dipping sauce.