Prepare draining station by lining a baking sheet with several paper towels and top with a wire cooling rack.
Cut onions into ¼ inch rings.
Heat frying oil to 375 degrees Fahrenheit.
Mix rice flour (1 ½ cups), cornstarch (½ cup), cornmeal (¼ cup), paprika (2 tsp), onion and garlic powders (1 teaspoon each), salt (1 ¾ tsp), cayenne pepper (pinch, optional), sugar (1 tsp) until well blended.
Whisk in buttermilk (½ cup), egg, and club soda (¾ cup) until batter is combined.
Dip rings, a few at a time into batter, making sure they're entirely coated, and shaking off excess.
Carefully place rings in hot oil, and fry in batches of 7-8 rings for 1-2 minutes until they are golden brown. Allow room in between frying rings.
Use a slotted spoon or spider skimmer to remove rings from oil and transfer to the wire rack draining station. Don't over crowd the rings.