I'm cheating here. I made onion rings
while doing a batch of tempura rather than making them
by themselves. But, what the heck.
What you need:
Tempura batter or onion ring batter
A white onion
or vegetable oil for deep frying
I used storebought tempura batter, myself.
I may Google up a recipe later. The panko is optional,
but it adds a very nice crunch.
So, make the tempura batter according
to the box's instructions, saving some of the dry mix aside.
(You may only want to use half a box of batter
unless you're making a BIG batch of rings.) Heat the
oil up in a pan deep enough to immerse the rings, and
cut the onion up and separate it into rings.
Next, dip each ring in the dry mix (which
will help the batter stick), then into the batter, then
cover it in panko, and finally put it into the oil.
Repeat, repeat, repeat. Take the rings out as they cook;
if you use panko they'll be golden brown. Drain on paper
towels. Serve with ketchup.