Cut Yellow Onion (1) into 1-inch thick rings.
Into a mixing bowl, add All-Purpose Flour (1 cup) plus 2 tablespoons, Baking Powder (1/2 teaspoon), Ground Black Pepper (1 teaspoon), and Salt (1 teaspoon). Whisk together.
Add 3/4 of the Club Soda (1 cup). Mix it, then add the rest. Mixture should have the texture of a thick pancake batter.
Coat each onion ring in the batter, then in the Panko Breadcrumbs (2 cup).
Place finished rings onto a baking sheet. Let them sit in the fridge for 15 minutes.
In a pan, heat Cooking Oil (as needed) to 325 degrees F (162 degrees C). Fry onion rings until golden brown on one side, then flip and let brown on the other side. The whole process should take 3-4 minutes.
Transfer the onion rings to a wire rack to drain excess oil. Let cool slightly before eating.