How to Caramelize Onions Properly
Caramelised onions are one of the most transformative cooking techniques. Raw onions are sharp and pungent; after 45 minutes of low heat, they become sweet, jammy, deep golden, and almost unrecognisably delicious. They elevate everything — burgers, pasta, steaks, soups, flatbreads, and grilled cheese.
Total time: 50 min · Servings: About 1 cup
Ingredients
- 4 large yellow onions (about 800g — they cook down to about 1/4 of their raw volume)
- 2 tbsp butter
- 1 tbsp olive oil
- 1/2 tsp salt
- Optional: 1 tsp balsamic vinegar or 1 tbsp brown sugar (at the end, for extra depth)
Instructions
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Slice the onions: Peel the onions, halve them root to tip, then slice into thin half-moons (about 3–4mm thick). Don't dice — long slices caramelise more evenly.
Tip: Root-to-tip slices hold together better during the long cooking process than crosswise slices. -
Start cooking: Heat butter and olive oil in a large, heavy-bottomed pan (cast iron or stainless steel is ideal) over medium heat. Add all the onions — the pan will look overfull, but they shrink dramatically.
Tip: Start with medium heat to get the initial moisture out. The pan should sizzle gently, not aggressively. -
Season and wait: Add the salt (this draws out moisture) and stir to coat. Spread the onions evenly. Now: reduce heat to medium-low and cook, stirring every 5–7 minutes.
Tip: After 10 minutes, the onions will look wilted and translucent. This is not caramelised — this is just the starting point. -
Develop colour: After about 20 minutes, the onions will start turning light golden. Reduce heat to low if they're colouring too fast. Stir every 3–4 minutes now, scraping any browned bits from the bottom of the pan back into the onions.
Tip: Those browned bits on the pan bottom (the fond) are concentrated flavour. Stir them back in — don't let them burn. -
Deglaze if needed: If the pan looks dry and things are starting to stick or burn, add 1–2 tablespoons of water. It sizzles, dissolves the stuck bits, and keeps things moving. You may need to do this 2–3 times.
Tip: This small amount of water is a rescue technique. Don't add a lot — just enough to loosen the fond. -
Finish: After 40–50 minutes total, the onions should be deep golden brown, sweet, and reduced to about 1/4 of their original volume. They should be jammy and soft, not crispy. Add a splash of balsamic vinegar if desired and stir.
Tip: Taste one. If it's sweet and deep and complex, they're done. If it still tastes like a cooked onion, keep going.
Pro Tips
- Real caramelised onions take 40–50 minutes. Any recipe that says 10–15 minutes is making sautéed onions, not caramelised ones. The Maillard reaction that creates the deep sweetness and colour requires sustained low heat.
- Make a big batch — they keep in the fridge for a week and freeze for 3 months. Having caramelised onions ready is a superpower.
- Use them on: grilled cheese, burgers, steaks, pasta (with balsamic and Parmesan), pizza, flatbreads, omelettes, soups (especially French onion soup), and as a side to roasted meats.
Frequently Asked Questions
Can I caramelize onions faster?
Adding a pinch of baking soda at the start speeds up the Maillard reaction and can reduce the time to about 25–30 minutes. Use 1/4 tsp for 4 onions. The texture will be softer (more jammy) but the flavour is still excellent.
Why are my caramelised onions bitter?
The heat was too high and they burned instead of caramelised. Burned onion bits taste acrid. Low and slow is essential. If dark spots appear too quickly, reduce the heat immediately.
What type of onion is best for caramelizing?
Yellow onions are the classic choice — they have a balanced sweetness and flavour. Sweet onions (Vidalia, Walla Walla) work but can become TOO sweet. Red onions caramelise well but turn a darker, less appetising colour.
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