To make the onion petals, in a large, deep skillet, heat about 3 inches of oil until a thermometer reads 350°. Line a metal tray with paper towels.
Add flour to a bowl. Add the onions and toss, coating them well. Shake off the excess. Dip the petals into the batter and coat well. Carefully add the petals, one by one, to the hot oil, making sure not to overcrowd the skillet. Fry until golden brown and crispy. Remove with a slotted spoon. Drain on paper towels. Season with salt and pepper while still hot. Serve at once. Serves four.