Peel the 2 large onions and slice them into thick rings. Separate the rings carefully, keeping them intact.
In a medium bowl, combine the 1 cup flour 2 tablespoons cornstarch, 1 teaspoon baking powder, 1 teaspoon salt, ½ teaspoon black pepper, ½ teaspoon paprika, and ½ teaspoon garlic powder.
In a separate bowl, whisk together the ½ cup milk and 1 large egg until smooth.
Take each onion ring and first dip it into the dry flour mixture. Shake off any excess. Next, dip the onion ring into the wet milk‑egg mixture. Then, dip it back into the dry flour mixture again, pressing gently to ensure the coating sticks well.
Preheat the air fryer to 375°F (190°C) for 3‑5 minutes. Lightly spray the basket with cooking oil to prevent sticking.
Place the coated onion rings in a single layer in the air fryer basket. Lightly spray the tops with cooking oil. Air fry for 8‑10 minutes, flipping halfway through, until golden brown and crispy.
Remove the onion rings from the air fryer and serve hot with your favorite dipping sauce like tartar sauce, ketchup, or spicy mayo.