Start by peeling the large onion and trimming off the top. Place the onion cut-side down on a cutting board. Carefully slice the onion into 12-16 wedges, making sure not to cut all the way through the bottom so it stays intact and can bloom when cooked.
In a large bowl, whisk together the flour, 2 teaspoons of McCormick seasoned salt, black pepper, and garlic powder. In a separate bowl, pour in the buttermilk.
Dip the prepared onion into the buttermilk, ensuring it is fully coated. Allow excess buttermilk to drip off. Then dredge the onion in the seasoned flour mixture, coating each petal well. For extra crunch, repeat the dipping and dredging for a double coating.
Heat vegetable oil in a deep fryer or heavy pot over medium heat until it reaches about 350°F (175°C).
Gently lower the coated onion into the hot oil, cut side down. Fry for 5-7 minutes or until golden brown and crispy. Remove with a slotted spoon and drain excess oil on paper towels.
In a small bowl, mix together sour cream, ketchup, 1 teaspoon McCormick seasoned salt, ground red pepper, horseradish, and paprika until well combined. Adjust seasoning to taste.
Place the fried onion on a serving platter and serve hot with the zesty dipping sauce on the side. Enjoy!