Cut the top off of the Vidalia onion, then peel it. Discard the skin and top, then slice the onion into 1/4 inch to 3/8 inch round rings. Save any leftover onion for another recipe or to make stock. Place the onion rings in a bowl and set them aside while you prepare the other items.
Place all of the ingredients in a large mixing bowl and combine them thoroughly. Set the bowl aside.
Place all of the ingredients, except for the buttermilk, in a large mixing bowl and combine them thoroughly. Add some buttermilk a few teaspoons at a time until the sauce reaches the proper consistency. Transfer the ranch sauce to a container with a lid and refrigerate it until the onion rings are finished.
Set up a three stage breading station to bread the onion rings. The first bowl should have one to two cups of unseasoned Wondra flour. Add two cups of buttermilk to the second bowl and use the breading you made previously as the third bowl. Work with a few onion rings at a time and dredge them in the Wondra flour, then dip the rings in the buttermilk. Pull the onion rings from the liquid, one at a time, and let some of the excess buttermilk drip off. Transfer each onion ring to the seasoned breading. Coat the rings evenly and place them on a parchment paper lined sheet pan.
Preheat the frying oil to 325 degrees°F (163°C). Work in batches and fry the onions rings for about three minutes until they're golden brown and delicious. Remember to flip each ring halfway through the frying process. This will ensure they cook evenly.
Serve the onion rings with ranch sauce and enjoy!