Caramelised Onion Tart with Wholemeal Olive Oil Pastry, and How to Caramelise Onions Using Minimal Oil or Butter


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Onions might seem a strange thing to write about for a Valentine’s post.  But there are ingredients in any love affair that are crucial to making the whole thing work: with people, they can be complicated and often baffling – especially to your friends – but with food it’s rather simpler: they are the things that make food taste more delicious. 

For me, one of these is onions. In particular, when they are sautéed or caramelised, and when I found a way of cooking them that made them taste amazing without using a bucketful of oil or a barrel of butter, it was like falling in love all over again. So they seemed the obvious thing to write about for the day earmarked to celebrate romantic love.* 

*Sponsored by Cadbury, Mars, and Interflora. 

I probably should admit that my relationship with onions got off to a bad start. My first encounter was with a substance called Boiled Onion Sauce.  The exact details of this revolting concoction have mercifully been removed from my brain and the perpetrators are dead.  At least I certainly hope so.  But until I was nine, I was firmly of the belief that onions were a form of cruel and unusual punishment inflicted on children for no other reason than it was lunchtime.

Luckily I had a godmother in Strasburg who introduced me to Alsatian Onion Tart.   She announced its arrival at breakfast.  We would be having it for dinner, she said, looking pleased, as if she was telling us glad tidings. I can still remember the moment when, in place of the gloopy, foul-smelling mess I’d been dreading, what arrived on the table was a miraculous vision of golden, caramelized onions sitting on a buttery, crumbly pastry, which tasted as delicious as it looked. 

I hadn’t realised that the problem wasn’t the onions, but the way they’d been treated. Or that treating them differently could turn them from something demonic into something divine. 

A bit like people I suppose.

Although I don’t think people would taste that good, however you cooked them.

Caramelised or Sautéed?

These terms are often used interchangeably, which is fair enough, given that either are a bit of both.   However, I tend to think of sautéed as cooked at a slightly higher temperature for between 10 and 20 minutes, with result glistening and golden brown, and caramelised as cooked at a lower temperature for between 30 and 60 minutes, by which time the onions have lost all sense of personal identity, are soft and densely sweet, and probably fairly dark.

N.B. Have nothing to do with instructions that call for cooking onions till soft for 2 minutes… or 5 minutes: it’s the culinary equivalent of, ‘my wife doesn’t understand me’. Onions do not cook in 5 minutes.

Practically Pointless Caramelised and Sautéed Onions

Quantity of oil or butter: 

1 teaspoon for up to 300g / 2 medium onions, 

Plus ½  – 1 teaspoon of oil for the pan. 

You can use more oil or butter than this, but you cannot use less.  

Using 2 teaspoons per 300g does make them fractionally nicer, but I am coming round to the view that using more oil than that doesn’t actually make much difference: it is the natural sweetness and juiciness of the onions – and caramelising it – that make them taste so divine, rather than the quantity of oil or butter*. 

*I would like to make it clear that I am a HUGE fan of both, and I only avoid them in big quantities because they are very calorie dense.


  1. Finely slice the onions with the grain rather than across it. Put them in a bowl and add the oil.
  2. Use your hands to mix the oil into the onions, ensuring that they are really, really well-coated.  It is this thorough mixing that makes it possible to use so little oil and still get deliciously sautéed or caramelised onions.   
  3. If using butter, melt it first, before adding it to the onions.
  4. Add a pinch of salt at the same time as the oil: it draws out the juice, which helps with the caramelisation, and brings out the sweetness of the onion  (think salted caramel).
  5. Depending on size of the pan, heat ½  – 1 teaspoon of olive oil in the pan till it has spread out to cover the base, so you are not putting cold onions straight onto hot metal or non-stick coating.  


  1. Heat the oil on a middling heat until it covers the base of the pan, and add the onions. Stir them, put a lid on the pan, and turn the heat down a tad.
  2. Keep the lid on for at least five minutes – it helps the onions cook without drying out. Stir fairly frequently.
  3. After 5 – 10 minutes, take the lid off to condense the juices and cook till they are as brown as you want, and have the right amount of bite – or lack of it – for whatever you have in mind for them. The exact timing will depend on the onions, the heat, the pan, and whether you wander off and start doing something else.


  1. Heat a teaspoon of oil in a pan on a low to medium heat until it has spread out to cover the whole of the base.
  2. Add the onions. When they start to sizzle a little, stir, put a lid on them, and turn the heat right down.
  3. Leave them on a low heat until the juices are beginning to come out – about 10 minutes.
  4. For the next 20 – 40 minutes (depending on onions, heat, and pan), stir from time to time, and turn the heat up a bit and down a bit, depending on whether you want to encourage them or stop them burning or drying out.
  5. Towards the end, take the lid off and turn the heat up a little to reduce the liquid and intensify the sweetness. Stir often at this stage. It would be tragic after all this time to burn the onions.


Caramelised Onion Tart

Serves 4

6 points per serving

This onion tart is nothing like the one I ate in Strasbourg but it’s not nearly so ruinous to a downsizing regime as a quiche or Alsatian onion tart.  It is simply caramelised onions and wholemeal pastry made with olive oil.  It doesn’t sound much, but I have been asked to dine with kings* so long as I promise to bring one with me.

* Well, they would if they had tasted it.

It is fabulously easy to make, and the whole thing is dairy free and vegan.   

600g red onions, caramelised with 2 teaspoons oil plus 1 for the pan, and a pinch of salt.

140g wholemeal pastry

A few sprigs finely chopped rosemary  

 For the pastry

100g wholemeal flour

40g olive oil

Pinch of salt

2 teaspoons chia seeds (optional)

A pinch of cumin seeds (optional)

2 – 3 tablespoons (40ml) water


While the onions are cooking, heat the oven to 200º / gas mark 6, and make the pastry 

  1. Put all the ingredients in a bowl and mix it with your hands like a mud pie.  Add as much water as needed to make a soft dough. Gather it into a ball.
  2. Put the ball of pastry in the middle of a 20cm flan ring and press it over the base and sides.  DO NOT try and roll it out  – it just falls to pieces.
  3. Bake it blind for 15 – 20 minutes
  4. Pile the onions onto the pastry, sprinkle over the chopped rosemary, and bake in the oven for about 30 minutes  

Diva Notes:


I use wholemeal flour from Pimhill Farm  The farm has been organic for 70 years, and the taste and texture of the flour is really excellent for pastry – and I also use it in my bread.  

Do not substitute plain flour for wholemeal: the onions need the nuttiness and depth of flavour from the wholemeal.


I press this pastry by hand into the flan ring because it doesn’t roll out without falling to pieces.It is time consuming but much less faff (no floured surfaces to make a mess in the kitchen), and rather fun. 


I used 600g of red onions because that’s what I had in my fridge. You can use other onions, and more or less of them, depending on what you have in your fridge. Slice them thinly, and with the grain. Don’t forget to add the salt when you are cooking them.


I used chia seeds because that’s what I had.  Feel free to use other seeds or none.