In a large bowl, whisk together flour, baking powder, paprika, salt and white pepper.
Cut the tip (not the root) off of the onion with a sharp knife. Peel off the brown skin, then carefully make 1/2" slices along the onion. Pop out the rings, discarding any extremely small ones or any that broke.
Coat the onion slices in the flour a handful at a time, then place on a wire rack with paper towels underneath (to catch excess flour). At this point you can heat a couple of inches of oil in a suitably sized pot/pan to 190C/375F.
Pour the cold beer into the leftover flour and gently whisk to combine. Don't beat the hell out of it, or you will burst all of the bubbles. Whisk until just combined. A few lumps in the mixture are fine. The consistency should be ever-so-slightly thicker than heavy/double cream. You can adjust slightly with beer/flour if needed.
Grab a handful of the onion rings and submerge them into the batter. One by one, pluck 4-5 of them out and carefully add to the hot oil, separating any that instantly stick. Allow to fry for 2-3mins, flipping once, or until golden and visibly crisp. Remove and place on your first wire rack with paper towels underneath. Repeat with remaining onion rings. Try to work quickly (but also safely) so the batter stays as cold as possible.
Sprinkle/ toss the onion rings with salt then serve and enjoy!