Red onion

Slice it thinly and soak it in cold water for 10–15 minutes, then drain and dry it well. For a tangier result, toss the slices with vinegar or lemon juice and a pinch of salt instead.

Slice it evenly and cook in a little oil or butter over a low heat for about 25–35 minutes, stirring regularly. A splash of water helps loosen the browned bits if the pan starts to catch; add sugar only if you want extra sweetness.

Yes. Pack thin slices into a clean jar and cover with hot vinegar, a little water, salt and sugar; leave for at least 30 minutes before serving. Keep the jar in the fridge and use the onions within about two weeks.

Wrap the cut surface or put the onion in an airtight container and refrigerate it; use it within a few days. Keep whole onions somewhere cool, dry and well ventilated, away from potatoes.

It works raw in salads, tacos and burgers, and cooked in chutney, curries, traybakes and onion tart. Red onion also gives Greek salad and salsa a crisp, peppery bite.

Yes: use the same amount in most cooked dishes. Red onion is usually sharper raw and can lose its vivid colour when cooked, while yellow onion tends to give a more familiar savoury flavour in soups and sauces.

Their energy and fibre are very similar: red onion has 35 kcal and 2.5 g of fibre per 100 g, compared with 36 kcal and 2.6 g in yellow onion. The difference is small enough that flavour and how you plan to use it are better reasons to choose one.

Its natural pigments can change colour when they meet alkaline ingredients, such as bicarbonate of soda, or certain minerals in water. A little vinegar or lemon juice adds acidity and helps keep the colour redder.