1. Place onions in a large bowl filled with cold water and soak 10 minutes.

2. Heat 2 inches of oil in a deep, heavy-bottomed pot to 365 degrees.

3. In a medium bowl, whisk together flour, cornstarch, baking powder, and salt. Whisk in ice-cold water and place batter bowl over a bowl of ice.

4. Drain Vidalia onions and dry thoroughly between layers of paper towels.

5. Working one handful at a time, dip onions in batter, allowing excess to drip back into bowl, and gently place in oil. Fry, turning once, until crisp and golden, 3 minutes. Transfer to a paper towel-lined tray to drain and sprinkle with salt to taste.