Preheat the oil in a pan or saucepan over medium heat. If you own an oil thermometer, it should read 180°C/350°F.
Dunk the onion rings one by one in the batter and take them to fry immediately. Always be careful not to burn yourself; get the ring close to the surface first and let go once it's had contact with the surface to prevent splattering.
Let them fry for 2-3 minutes, flipping them halfway through.
Remove them from the oil and place them in a bowl with kitchen paper to absorb the excess fat.