Preheat the oven to 220°C. Place parchment paper onto 2 baking sheets and set aside.
In a small bowl, combine the flour, paprika and 2 teaspoons salt. In another bowl or shallow dish, whisk together the buttermilk and eggs. Add half of the flour mixture to the buttermilk and beat until smooth and thickened.
In a separate bowl, combine the panko, olive oil and remaining 2 teaspoons salt.
Lightly dredge the onion rings in the flour mixture and then drop into the buttermilk. Drain the excess batter and then dredge in the panko mixture.
Arrange on the prepared baking sheets in a single layer. You can place smaller rings inside bigger rings if necessary, just make sure there is space between them. Then place in the oven. Cook until golden brown, 14 to 20 minutes. Halfway through the cooking time, flip over each onion ring to ensure even crisping and browning.
Recipe courtesy of Jeff Mauro