Start by peeling your onions and cutting them into thick rings. Aim for about ¼ inch thickness to ensure they fry evenly. Discard the ends and any tiny bits in the middle that won’t hold together.
In a mixing bowl, combine the whey protein isolate, garlic powder, paprika, flaked salt, and black pepper. In another bowl, whisk together the egg, Dijon mustard, and sparkling water until well blended. Gradually add the dry ingredients to the wet mixture, stirring until a smooth batter forms.
In a deep frying pan, heat your choice of oil over medium-high heat. You want enough oil to submerge the onion rings, so aim for about 2 cups. To check if the oil is ready, drop a small amount of batter into the oil; it should sizzle and rise to the top.
Working in batches, dip each onion ring into the batter, allowing any excess to drip off. Carefully place the battered onion rings into the hot oil. Fry them for about 3-4 minutes on each side, or until they’re golden brown and extra crispy.
Once fried, use a slotted spoon to remove the onion rings from the oil and place them on a plate lined with paper towels to drain any excess oil. Serve them hot with your favorite dipping sauce, or enjoy them plain!
