I have tried about five recipes. All fell short, some fell flat, but I think I have a good one here and we ate the whole plate! If you like this recipe, see others at my website: mybestcookbook.wordpress.com
Cut onion rings and let sit for 30 minutes to dry. Meanwhile mix the dry ingredients with a whisk. Heat oil in a cast iron skillet to a depth of one inch. (sizzles when drops of water hit it)
Add the milk and egg to your flour mixture and whisk until fairly smooth. You are looking for a thick batter that will cling to the ring. Add ring and coat, then put in the oil, turn when browned and do the other side. The batter should remain covering the entire piece.
After the test ring you can adjust the batter by more milk or flour to get the right consistency. It should be a bit thinner than a pancake batter, but not runny.
Note: I use wooden skewers to fish my rings out of the batter, and a clean one to turn over in the fry pan and retrieve from the oil when done.
Remove your rings to a jelly roll pan, lined with paper toweling with a rack on top. Let them drain, and then keep them in a 250 oven to remain crisp until ready to eat.