Using the mandoline, cut the onions into thick slices.
Separate the slices into rings and put them in cold water.
Mix the paprika, black pepper, white pepper powder, and salt with the flour and cornstarch. See note 1.
Take the onions out of the water and dredge them in the flour.
Gently shake off the flour and fry the rings in vegetable oil over medium to high heat until golden brown. Make sure to not crowd the pan. See note 2
Drain onto a paper towel to absorb any excess oil.
Add to your burger and enjoy.
Video
Notes
The dredging mixture is a 1:1 ratio of all-purpose flour to cornstarch.
Make sure the oil is hot (if the oil is too hot however, the onions will burn) before you fry your onion rings, or else they will end up soggy. It is also important not to overcrowd your pan.