Prepare the batter: put the flour in a bowl, make a well in the center to crack the egg, add the oil, a pinch of salt and pepper.
Mix vigorously, the batter should be smooth, without lumps and of the right consistency.
Let it rest for one hour.
Peel the onions and cut them into rings not too thin.
Soak them in cold water for about half an hour.
Drain them, dry well, and after quickly passing them through the batter, fry in plenty of hot oil.
Remove with a slotted spatula, drain on paper towels, sprinkle with salt and pepper.
Serve hot.