The Great Caramelised Onion Myth

Almost every recipe that calls for caramelised onions says it takes "10–15 minutes." This is, bluntly, wrong. True caramelisation — where onions transform into sticky, golden, deeply sweet jammy strands — takes 45 minutes to an hour over low heat. Rushing it gives you softened onions. Nice, but not the same thing.

Understanding why this matters will change the way you cook.

What Actually Happens During Caramelisation

When onions cook low and slow, two separate chemical processes occur:

  • Water evaporation: Onions are about 90% water. Much of that water must cook off first, which is why they shrink so dramatically.
  • The Maillard reaction and caramelisation: Once water is reduced, the natural sugars in onions begin to brown. This produces hundreds of new flavour compounds — what you taste as that complex, sweet, savoury depth.

Crank the heat to rush things and you skip the slow water evaporation phase and jump straight to burning.

What You Need

  • 3–4 large yellow or white onions (they reduce dramatically)
  • 2 tablespoons butter or olive oil (or a mix of both)
  • Pinch of salt
  • Optional: splash of balsamic vinegar, white wine, or a pinch of sugar to deepen colour

The Method, Step by Step

  1. Slice onions thinly and evenly — about 5mm thick. Uneven cuts lead to uneven cooking.
  2. Heat your pan over medium-low — a wide, heavy-bottomed pan or Dutch oven is ideal. Add butter/oil.
  3. Add onions and salt. Toss to coat. The salt draws out moisture and accelerates the process slightly.
  4. Cook low and slow, stirring every 5 minutes or so. They'll wilt and shrink in the first 20 minutes.
  5. After 30 minutes, they should be soft and turning golden. Keep going.
  6. At 45–60 minutes, they should be deep amber, jammy, and reduced to roughly a quarter of their original volume.
  7. Optional deglaze: Add a splash of balsamic or wine, scrape up any fond from the bottom, and cook for another 2 minutes.

Common Mistakes to Avoid

  • Too much heat: The number one mistake. If onions are sizzling aggressively, turn it down.
  • Not enough onions: They shrink by 75%. Start with more than you think you need.
  • Thin pan: Thin pans create hot spots that burn onions unevenly. Use a heavy pan.
  • Skipping the scraping: Those browned bits on the bottom are pure flavour. Scrape them up with each stir.

How to Use Caramelised Onions

The effort pays dividends across countless dishes:

  • Spread on a grilled cheese or burger
  • Stir into pasta or risotto
  • Top a homemade pizza
  • Fold into frittatas or quiches
  • Base for French onion soup
  • Layer into a tart or flatbread

Make a big batch on the weekend and store in the fridge for up to a week — or freeze in ice cube trays for an instant flavour boost whenever you need it.