First, peel the onion, slice into half-inch thick rings, and separate.
Next, whisk pancake mix and beer together in a small bowl until well-combined. In the meantime, heat about three-quarters inch to an inch of vegetable oil in a deep cast iron frying pan over medium-high heat.
Once the oil is very hot, start working in batches of 3 to 5 onion rings. One by one, coat the onion rings in a thin layer of batter, letting the excess drip off before it goes in the pan. Once the pan is full (make sure not to overcrowd it), gently agitate the oil with a fork to help the batter solidify all around the onion rings. After about 30 seconds to 1 minute, once the bottoms of the onion rings are slightly golden, flip them gently with a fork. Continue frying for another 15 to 30 seconds or so, until the onion rings are a deep golden-brown all the way around.
Transfer the cooked onion rings to a plate lined with paper towels to drain the excess oil. Continue working in batches until all the onion rings are fried. Let cool at least 5 minutes before serving.
Notes
What kind of beer to use: The beer flavor comes through in these onion rings, so choose a beer you love! You can use a light lager for a more traditional onion ring, or a darker option like Guinness for a sweeter, more flavorful onion ring.Tips for frying onion rings: Agitating the oil right away helps the top layer of batter solidify on the onion rings so that it doesn't come off when you flip them. Since the onion rings will float in the oil, the tops won't be submerged in oil right away, so this step really helps!We also recommend working quickly, which is why we like to fry these in batches of 3 to 5 onion rings at a time. Frying is fast, and if you're not careful you could end up with burnt onion rings. To help make sure you can work efficiently, set up your workstation ahead of time with all the necessary tools and equipment easily within reach.Prep ahead: If you want to make these onion rings for a party, you can make them up to an hour in advance and they'll still taste super fresh! Just leave them out at room temperature and reheat in an air fryer at 350 degrees F for about 5 to 10 minutes.Serving suggestions: Beer battered onion rings are a great game day snack served with your favorite dips! Pair them with ketchup, ranch, chipotle mayo, or even BBQ sauce for a tasty treat. Or, serve them as a side dish with your favorite burger.