Begin by peeling the large yellow onion and slicing it into thick rings, about 1/2 inch wide. Gently separate the rings and set them aside.
In one bowl, whisk together the all-purpose flour and a pinch of salt. In a second bowl, beat the large egg. In a third shallow dish, mix the Panko breadcrumbs with the melted butter until well combined.
Take each onion ring and first dip it into the flour mixture, ensuring it’s completely coated. Shake off any excess flour, then dip it into the egg, allowing any extra to drip off. Finally, roll the onion ring into the Panko breadcrumb mixture, pressing gently to adhere. Repeat until all rings are coated.
In your deep frying pan or dutch oven, heat the vegetable oil over medium heat until it reaches 350°F (175°C). You can test the oil by dropping in a small piece of breadcrumb; if it sizzles, it’s ready.
Carefully add a few onion rings to the hot oil, ensuring not to overcrowd the pan. Fry for about 2-3 minutes on each side or until they are golden brown and crispy.
Use a slotted spoon or tongs to remove the onion rings from the oil and place them on a paper towel-lined plate to drain excess oil. In a large bowl, toss the hot fried rings with the hot sauce until they are evenly coated.
Transfer the coated Buffalo Onion Rings to a serving platter. They are best enjoyed fresh and hot, perhaps with a side of ranch or blue cheese dressing for dipping.