Peel the onion, cut in half and cut into wafer-thin slices. Heat the oil in a pan. Heat the blueberries with the sugar in a saucepan.
Put the onion slices in the oil and fry them lightly until they get a golden sheen. Add the berry-sugar mixture complete with the juice and the white wine vinegar. Simmer, stirring constantly, until the onions are firm to the bite. Finally, season with salt and pepper.