The Art of Patience: Mastering a Caramelised Onion Tart with a Short Pastry Base

When it comes to baking, it's hard not to feel fulfilled creating a dish that requires extra love and attention. One standout option is caramelised onion tart—a deliciously rich, but indulgent treat using minimal ingredients, that showcases the sweet, savoury goodness of onions in the shortest of short pastry cases, without that eggy quiche vibe. This is a very, very slightly tweaked version of an old Valentine Warner recipe, and let me tell you the results for his short crust pastry are insanely good! This is not a quick bake, it's a labour of love and patience, but this dish will reward you for your work.

The Magic of Caramelised Onions

Caramelised onions are truly the star of this dish. Transforming raw onions into sweet, tender morsels requires care and patience, but the result is well worth the effort. You will need 9 large white onions—a quantity that may seem intimidating if you are like me and are a teary mess after chopping only one and half onions, yet, as you chop, I find you start to become immune to their tear-inducing effects!

The onions need to be finely chopped in the Caramelised Onion Tart, then cooked until meltingly tender, and as Valentine Warner recommends, this really will take about 2 hours.

Caramelised Onion Tart - The Recipe

Ingredients

For the Pastry

340g plain flour

200g cold butter, cubed

2 egg yolks

A splash of cold water

For the Onion Filling

9 Large white onions, finely chopped

150g butter

2 tbsp light brown sugar

100mls cider vinegar

2 tsp Dijon mustard

2 tsp flaky sea salt

50g finely grated parmesan

Method:

Start by melting your melting you butter in a large frying pan on a low heat. Add your finely chopped onions and cook over a low heat for around 2 hours, stirring occasionally, until meltingly and completely soft.

Preheat the oven to 190C / 375F.

In a large mixing bowl, combine the flour and cubed butter. Use your fingertips to rub the butter into the flour until the mixture resembles coarse breadcrumbs. This step is essential for achieving a light, flaky texture.

Then, add the egg yolks and a splash of water, mixing until the dough starts to come together. Be cautious not to overwork it—keeping the pastry light and airy is key.

Once ready, wrap your dough in cling film and refrigerate for at least 1 hour. This resting period lets the gluten relax, considerably easing the rolling process later on.

After 1 hour remove the dough from the fridge and roll out into your tart tin. Prick the base all over and trim the excess dough around the edges. It's now time to blind bake the tart. Line with grease proof paper and add baking beans, place in the oven and bake for 20 minutes. Carefully remove from oven and remove greaseproof paper and baking beans. Place the case back in the oven and bake for a further 10 minutes. Carefully remove from the oven and place to one side.

Once your onions are completely soft, it's time to elevate their flavour profile. Turn up the heat to high and stir in the cider vinegar, light brown sugar, and 2 teaspoons of Dijon mustard to the pan along with the sea salt. Continue to cook for an additional 20 minutes, or until the vinegar has evaporated and the onions are taking on a beautiful golden colour.

Remove the onions from the heat and tumble the onions into your prepared case, spreading the mixture evenly across the base. For an extra touch, sprinkle 50g of freshly grated Parmesan cheese on top.

Return the tart to the oven and bake for an additional 25-30 minutes, or until the top is golden brown and bubbling.

Allow the tart to cool for several minutes before slicing. It can be enjoyed warm or at room temperature, making it a versatile dish suitable for any occasion.