1. In a mixing bowl, mix together the flour, salt and baking powder.
2. In another bowl, whisk together the beer, egg and vegetable oil. Stir this mixture into the flour mixture until it is well combined.
3. Peel 1 large onion and then cut it into 1/8 inch slices and separate into rings. Place the rings on a plate and set aside.
4. Heat the oil in a frying pan and once the oil is hot, dip these onion rings into the batter and then deep fry them in the hot oil. Cook on both sides for about 4-5 minutes or until golden brown and crispy.
5. Once done, remove the crispy onion rings from the oil and place them onto paper towels to absorb any excess oil.
6. Serve these beer battered onion rings with a mayo or ketchup dip.