Peel the large yellow onion and slice it into thick rings about ½ inch wide. Separate the rings gently and set aside.
In a small bowl, whisk together the melted butter and hot sauce until smooth. Set aside for coating later.
Place the flour in a wide bowl. In another bowl, beat the egg until smooth. In a third bowl, place the Panko breadcrumbs.
Pour the vegetable oil into a frying pan or pot and heat over medium-high heat to about 350°F (175°C). Test by dropping a small piece of bread; it should sizzle and turn golden in about a minute.
Dredge each onion ring first in flour, shaking off excess, then dip in beaten egg, and finally coat thoroughly with Panko breadcrumbs.
Carefully place coated onion rings into hot oil in batches. Fry 2-3 minutes per side until golden brown and crispy. Remove with slotted spoon and drain on paper towels.
Toss the warm fried rings gently in the buffalo sauce mixture until well coated.
Serve hot with your favorite dipping sauce, such as ranch or blue cheese, or alongside burgers or sandwiches.
