1. Preheat oven to 200°.

2. Clip a candy thermometer onto the side of a 4-quart Dutch oven; add oil to pan. Heat oil to 385°.

3. While oil heats, weigh or lightly spoon flours into dry measuring cups; level with a knife. Combine flours, chili powder, and baking soda in a medium bowl. Gradually add club soda, stirring with a whisk until smooth.

4. Dip onion rings, 1 at a time, in batter, coating completely. Add to hot oil. (Do not crowd pan.) Fry 1 minute on each side or until golden, maintaining temperature of oil at 375°. Drain onion rings on a paper towel–lined jelly-roll pan. Place pan in oven and keep warm at 200° until ready to serve. Combine salt, garlic powder, and black pepper. Sprinkle onion rings evenly with salt mixture just before serving. Serve with ketchup, if desired.