How to make Perfect Caramelised Onions

A quick and easy recipe for Caramelised Onions - soft, syrupy, sweet and almost nutty with so many possibilities!
Caramelised Onions

Estimated reading time: 3 minutes

You can watch my video tutorial on this at How to make Perfect Caramelised Onions.

Caramelised Onions – soft, syrupy, sweet and almost nutty with so many possibilities! In sandwiches, on salads, tarts, pizza, canapé topping, the list is as lengthy as your imagination.

While cooks may differ slightly in their approach, the general rule in caramelising onions is the same: sliced onions cooked slowly and on low heat. I tend to lean towards medium low – low heat and go for a total of 45 minutes on the hob. The result? Sheer heaven!

Caramelisation is a chemical process in which the sugars are heated and encouraged to break down to form new compounds which give us that signature caramelised brown colour and sweet aroma. In caramelising onions, we have another action coming into play and that’s the Maillard reaction, in which the sugars in the onions react with the small amount of proteins present in the onions. There are a couple of things we can do to aid the whole process, not so much in speeding it up but more of an enhancement of the final product. But more of that later.

Butter or olive oil? Both!

Butter, to me, is essential in this recipe, to give that all important nutty flavour at the end. But butter alone, always runs the risk of your onions browning too quickly, so we add a little olive oil to the mix to bring down our smoking point.

Back to the caramelisation. There are two things you can do to aid the caramelisation.

1. Add a pinch of sugar right at the start, immediately before you add the onions, no need to stir the sugar in before adding the onions. This will enhance the final sweetness and colour.

2. Add a pinch of sodium bicarbonate along with the onions. As mentioned before, when heated, the small amount of proteins reacts with the sugars in the onion and we get a Maillard reaction. Pronounced May-Yar (silent r), not Mel-Lard! There are many factors that affect the Maillard reaction but as far as we’re concerned here, heat and pH are the two that we can control.

Now, we don’t want to change the heat because low and slow, remember? That leaves us with the pH to play with. The more alkaline (higher pH value) the mix, the quicker the reaction. So what can we do? Add a pinch of bicarbonate soda, of course. Not only will this give you a darker shade of onions, but the onions will also be softer as the pectin reacts to the higher alkaline level and weakens. Simply put, the pectin is what holds the onion’s cell walls together – think crumbling pillars.

Bear in mind, these are optional extras. I don’t bother with the sodium bicarbonate and only occasionally bother with the sugar. In the video here, I’ve not gone with either.

If you like the recipe, don’t forget to leave me a comment and that all important, 5-star rating! Thank you!

And if you make the recipe, share it on any platform and tag me @azlinbloor, and hashtag it #linsfood

Lin xx

Caramelised Onions

A quick and easy recipe for Caramelised Onions – soft, syrupy, sweet and almost nutty with so many possibilities!
5 from 3 votes
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Course: Part of a meal
Cuisine: International
Keyword: onion
Prep Time: 5 minutes
Cook Time: 50 minutes
Total Time: 55 minutes
Calories: 69kcal
Author: Azlin Bloor


  • large white onions
  • 2 tbsp butter
  • 1 tbsp extra virgin olive oil
  • Water, Stock or Alcohol of your choice: cider, white wine


  • pinch of sugar
  • pinch of sodium bicarbonate


  • Heat the butter and olive oil in a large frying pan on medium low heat until the butter has melted.
  • Twirl it around to mix the two fats.
  • Add the onions and mix well, coating the onions in the fat.
  • Once the onions have heated through, after about a minute, turn the heat down to low.
  • Cook the onions for 20 minutes, stirring frequently, at which time, the onions will be a light golden colour.
  • Add a splash of liquid, stir well and continue cooking for another 20 minutes, at the end of which, the onions, will be soft, syrupy and a rich brown colour.
  • Add another splash of liquid, scraping the bottom and sides of the pan. This second deglazing will release all that sticky goodness to be absorbed back by the onions.
  • Cook for a final 5-10 minutes, turn the heat off and use as required.


Calories: 69kcal | Carbohydrates: 3g | Protein: 1g | Fat: 6g | Saturated Fat: 3g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 3g | Trans Fat: 1g | Cholesterol: 10mg | Sodium: 35mg | Potassium: 55mg | Fiber: 1g | Sugar: 2g | Vitamin A: 117IU | Vitamin C: 3mg | Calcium: 10mg | Iron: 1mg
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