Combine all ingredients for dipping sauce in a small bowl and set aside.
Peel and slice onions, then separate into individual rings.
Place in a large bowl and pour in buttermilk.
Chill 30 minutes.
Whisk cornmeal, baking powder, paprika, 3/4 cup flour and 1 1/2 tsp salt together in a medium bowl.
Whisking constantly, gradually add club soda and lager.
Place remaining 3/4 cup flour in a shallow bowl.
Pour one inch of oil into heavy skillet and heat over medium-high.
Working in batches (don't overcrowd the skillet or oil temperature will drop and onions may stick together), remove onion rings from buttermilk, dredge in flour (shaking off excess), then dip with a chopstick into batter, letting excess drip back into the bowl.
Fry, turning occasionally until crust is golden brown, puffed and crisp.
Transfer onion rings to a wire rack and season immediately with salt. Serve with dipping sauce on side.