Preheat the oil in a deep fryer to 350°F (180°C). Line a baking sheet with paper towels or place a wire rack on a baking sheet. Preheat the oven to 200°F (95°C)
Slice the onions 1/2 inch (1 cm) thick. Separate the slices into rings.
In a large bowl, whisk together the milk, eggs and salt. Set aside.
In another bowl, whisk together the flour, bread crumbs, curry powder and baking powder. Set aside half of the mixture in a separate bowl.
Working in batches, dip the onion rings in the milk mixture. Shake to remove any excess liquid. Dredge in the first bowl of the flour mixture, making sure to coat well. Dip again in the milk mixture, then dredge in the second bowl of the flour mixture. Place the coated onion rings on a baking sheet as you work.
Fry several onion rings at a time for 2 minutes or until golden brown, turning halfway through cooking. Watch out for splattering. Drain the onion rings on the paper towels. Season with salt and keep warm in the oven or serve with curried roast chicken (see recipe).