Preheat the vegetable oil to 170°C | 325°F in a large heavy-based saucepan or deep fat fryer.
In a large mixing bowl, whisk together the cornmeal, self-raising flour, bicarbonate of soda and salt. Stir in the onion.
Mix together the buttermilk and egg in a jug. Whisk the buttermilk mixture into the cornmeal mixture until well blended.
Drop 1 tsp of the batter into the hot oil for each hush puppy. Make sure the teaspoon is clean each time you drop the batter into the oil.
Turn the hush puppies to cook evenly and remove with a slotted spoon when golden brown in colour. Drain on kitchen paper and arrange in a serving bowl. Serve immediately.