How do you caramelise onions properly?

Caramelised onions are where kitchen honesty goes to die. Recipes promise them in ten minutes; onions disagree. What you get in ten minutes is softened, lightly browned onions, which are delicious but not the same thing. Real caramelised onions are slow, and the only trick is accepting that.

Slicing

Halve the onions through the root, peel, and slice from root to tip into even half-moons, about the thickness of a coin. Even matters more than thin: if some slices are paper and some are planks, the thin ones burn while the thick ones sulk. Yellow or brown onions are the classic choice; red onions work and go darker and jammier; white onions are a little sharper.

Make more than you think. They shrink dramatically.

The pan and the fat

Use the widest heavy pan you own. A wide pan lets moisture escape, which is what you want, and spreads the onions in a thick layer rather than a towering pile. Stainless steel or enamelled cast iron is ideal, because you can see the brown film forming on the bottom. Non-stick works but forms less of that flavourful film.

Fat: olive oil, butter, or both. Be generous; the onions should glisten, not squeak.

The heat and the stages

Start over medium heat with a pinch of salt, which draws out moisture and gets things moving. Then turn it down a notch. Here is what you will see:

• Softening. The onions turn limp and translucent and give off liquid. Stir now and then.
• Pale gold. The liquid has cooked away and the edges begin to colour. This is where most people stop.
• Light brown. A brown film builds up on the base of the pan. Stir more often now.
• Amber. The onions are soft, sticky and caramel-coloured, with a sweet, deep smell. Still a way to go if you want the full version.
• Deep brown and jammy. They collapse into a soft, glossy mass and taste sweet, savoury and almost meaty. Done.

The splash of water

When the film on the bottom of the pan turns dark brown, add a splash of water (or stock, or wine) and scrape it up with a wooden spoon. The onions soak it up and take on colour; this is deglazing on a small scale. Repeat whenever things start to catch. It lets you keep the heat lively without burning anything, and it is the closest thing to a shortcut that actually works.

If the edges go black and the smell turns acrid, the heat is too fierce. Turn it down, add water, and pick out any burnt bits.

Shortcuts we skip

• Sugar. Onions have their own sweetness. Sugar browns faster but tastes flatter and can burn.
• Turning the heat to maximum. You get burnt edges and raw middles.
• A crowded small pan. The onions steam and stew in their own liquid.

A pinch of bicarbonate of soda is sometimes suggested to speed up browning. In our hands it turns the onions soft to the point of mush, so we leave it out.

What to do with them

• On toast with goat's cheese or ricotta.
• Folded into a frittata or a torta salata.
• Stirred through lentils or white beans.
• On a pizza with a few olives and rosemary.
• In a toasted sandwich with sharp cheddar or fontina.
• As the base of an onion soup.