Start by slicing a large onion into discs between ¼" and ½" wide. Separate them into individual rings.
Prepare dredging stations: Set up two shallow bowls. In one, mix flour, cornstarch, water, smoked paprika, salt, pepper, and mixed herbs. Place Panko breadcrumbs in the second.
Dip each onion ring in the flour mixture, then into the breadcrumbs. Toss to coat evenly, pressing gently to adhere.
Heat oil: Heat 1- to 2-inches of oil in a skillet or deep fryer to 350-375°F over medium-high heat.
Fry onion rings: Working in batches, fry 4-6 rings at a time for 2-3 minutes or until golden brown and crispy. Transfer to a wire rack set over a baking sheet lined with paper towels to drain.
Serve with your favorite dipping sauce! Enjoy your crispy homemade onion rings with ketchup or any other sauce!