Add the onions and gently fry for 10 - 15 minutes or until softened and starting to turn golden. In a large pan over medium heat, heat about 2.5cm oil. 3. Heat the oil in a deep pan until it reaches 375. Soak the onions in the buttermilk for 30 minutes. Step 1 Heat the oil in large frying over a low to medium heat. Set aside and repeat with remaining onions. Now add to the softened onions and stir through until the onions … 1. In a shallow dish, add the flour, salt and pepper, and whisk to combine. Step 2 In a bowl add the ketchup, mustard, sugar and Worcestershire sauce and mix through. When oil is shimmering, add onions, working in batches, and fry until golden, about 2 minutes. 2.