Caramelised Onion & Feta Tart - Easy Quiche Recipe

This Caramelised Onion & Feta Tart will just make you want to go back for more! Tart, quiche, same same, one just sounds fancy. What I can tell you is that perfectly caramelised onions, a creamy egg filling, and salty crumbled feta in a golden shortcrust pastry case is one of the most DELICIOUS things you will ever eat.

Recipe Details:

• Prep Time: 15 minutes
• Cook Time: 1 hour 10 minutes (including blind bake and caramelising onions)
• Total Time: 1 hour 25 minutes
• Serves: 6
• Difficulty: Easy
• Special Equipment: Tart tin, baking paper, baking beans or rice

This recipe is part of my YouTube video all about how to caramelise onions properly, and I promise, once you learn the technique, you'll want to put them in everything! The secret to making the absolute best caramelised onions is adding water and salt to the pan at the start. I know it sounds completely backwards, but stay with me, the water creates steam that softens the onions beautifully first, then as the water evaporates, the natural sugars are released and that's when the magic happens. Deeply golden, sweet, soft, and utterly incredible. Four whole onions go into this tart, and once they're caramelised down they take up surprisingly little space - which is also a brilliant trick for using up a big bag of onions without wasting a single one. 

Why You'll Love This Recipe

• Perfectly caramelised onions: The water-and-salt method gives you restaurant-quality caramelised onions every single time
• A great way to use up onions: Four whole onions go into this one beautiful tart, brilliant if you've got a big bag to work through
• Stunning but simple: Looks incredibly impressive, genuinely easy to make
• Totally versatile: Swap the feta for whatever cheese you love, or add other vegetables you need to use up
• Perfect hot or cold: Just as delicious the next day, deal for packed lunches and picnics

Ingredients

For the Tart Case:

• 1 tart tin lined with shortcrust pastry (shop-bought is absolutely fine!)

For the Caramelised Onions:

• 4 onions, sliced
• 200ml water
• 1 teaspoon salt
• A drizzle of oil (optional, to finish)

For the Filling:

• 4 eggs
• 100ml milk
• 100ml cream
• 100g cheese, grated
• 1 teaspoon wholegrain mustard
• Salt and pepper
• Feta cheese, crumbled, to top

Instructions

1. Blind bake the tart case: Preheat your oven to 180°C. Place a sheet of greaseproof paper into your lined tart tin and fill it with baking beans or uncooked rice. Bake for 15 minutes, then carefully remove the paper and beans and return to the oven for another 5 minutes until the base is lightly golden. This step stops you getting a soggy bottom, and there is nothing worse than a soggy bottom tart!

2. Caramelise the onions: Add your sliced onions to a large pan. Pour in 200ml of water and add 1 teaspoon of salt. Put the lid on and bring to a medium heat. The water will create steam that softens the onions beautifully from the start - this is the key to perfect caramelised onions! Once the water has mostly evaporated, remove the lid and stir on a medium heat, adding a drizzle of oil if you'd like more colour. Keep stirring and cooking until the onions are deeply golden, soft, sweet, and completely caramelised - around 45 minutes in total. Be patient, it's worth every single minute!

3. Make the filling: Crack 4 eggs into a bowl. Add the milk, cream, grated cheese, and wholegrain mustard. Season well with salt and pepper and whisk everything together until combined.

4. Fill the tart: Turn the oven up to 190°C. Spread the caramelised onions evenly across the base of your blind-baked tart case. Pour the egg and cream mixture over the top, making sure everything is evenly distributed.

5. Add the feta: Crumble feta cheese generously over the top of the filled tart. As much or as little as you like - I say the more the better!

6. Bake: Very carefully transfer the tart to the oven and bake at 190°C for 25 minutes until the filling is just set with a very slight wobble in the centre and the top is lightly golden. If you have a deeper tart tin, it may need a few extra minutes, keep an eye on it.

7. Cool and serve: Remove from the oven and allow to cool for a few minutes before slicing. Always best served warm straight out of the oven if possible. Cut a generous slice, get stuck in, and enjoy!

Chef's Tips

The water trick is everything: Adding water and salt to your onions at the start is the restaurant secret to truly perfect caramelised onions. Don't skip it! The steam softens them gently first so that by the time the water evaporates, the sugars are already released and caramelisation happens beautifully and evenly.

Be patient with the onions: Properly caramelised onions take around 45 minutes. If yours are done in 10 minutes, they're not caramelised, they're just softened. Real caramelisation takes time and the results are completely worth it.

Blind bake properly: Don't skip the blind bake or rush it. That pre-cooked pastry case is what stands between you and a soggy, undercooked bottom. Nobody wants that!

Don't overfill: Pour the egg mixture in carefully and don't fill it right to the very brim, leave a little room as it will puff up slightly in the oven. Carry it to the oven very slowly and carefully.

Check for doneness: The tart is ready when the filling is set around the edges but has just a slight wobble in the very centre, like a baked cheesecake. It will continue to firm up as it cools.

Shop-bought pastry is great: Using a shop-bought shortcrust pastry case saves time and the result is just as delicious. Focus your energy on those onions!

Substitutions & Variations

Different cheese on top: Blue cheese is incredible in this if you love it, crumble it on top instead of (or alongside!) the feta. Goat's cheese is another wonderful option.

Add vegetables: This tart is super versatile. Blanched and well-squeezed broccoli, wilted spinach, roasted peppers, or courgette all work beautifully alongside the onions.

Different cheese in the filling: Gruyère, cheddar, parmesan, or even a smoked cheese all work wonderfully in the egg mixture instead of or alongside regular grated cheese.

Add fresh herbs: A scattering of fresh thyme leaves over the top before baking is a classic pairing with caramelised onions and absolutely delicious.

Add bacon or lardons: Fry off some bacon lardons and scatter them through the onions before filling for a smoky, salty addition.

Storage & Reheating

Best served warm: This tart is absolutely at its best served warm, fresh from the oven. But honestly? Cold from the fridge the next day runs a very close second.

Storage: Cover and refrigerate for up to 3 days. It's brilliant for packed lunches!

Reheating: Reheat slices in the oven at 160°C for 10-15 minutes. You can microwave it in a pinch but the pastry will soften,  the oven is always better.

Freezing: You can freeze this tart once cooked and cooled. Wrap individual slices well and freeze for up to 1 month. Defrost overnight in the fridge and reheat in the oven.

Make ahead: The caramelised onions can be made up to 3 days ahead and kept in the fridge, which makes this a great recipe to batch cook when you've got a big bag of onions to use up!

Frequently Asked Questions

Q: Can I use a shop-bought pastry case? A: Absolutely yes! A pre-made shortcrust pastry case from the supermarket works perfectly. Just blind bake it as instructed (or follow the packet instructions) before filling.

Q: How do I know when the onions are properly caramelised? A: They should be deeply golden brown, completely soft with no crunch whatsoever, and taste sweet rather than sharp. If they still have any bite or are pale golden, keep going! True caramelisation takes around 45 minutes.

Q: My filling is still wobbly after 25 minutes. What do I do? A: Give it another 5-10 minutes and check again. If your tart tin is deeper than average it will take longer. The edges should be set and only the very centre should have a slight wobble, it will firm up as it cools.

Q: Can I make this ahead for a dinner party? A: Yes! You can make the whole tart the day before, refrigerate it, and reheat in a 160°C oven for 15-20 minutes before serving. Or make the caramelised onions ahead (they keep for 3 days in the fridge) and assemble and bake on the day.

Q: Can I make individual tartlets instead of one large tart? A: Yes! Use individual tart tins, reduce the blind bake time to around 10 minutes and reduce the final bake time to around 15 minutes. Keep a close eye on them.

Q: What can I serve this with? A: A simple green salad is the perfect accompaniment. It's also lovely with a bowl of soup for a more substantial meal, or served as part of a spread with other dishes.

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Enjoy!

Del x

This Caramelised Onion & Feta Tart is one of those recipes that looks completely stunning but is so much easier than you'd think. Perfectly sweet caramelised onions, a creamy egg and cheese filling, and salty feta in a golden pastry case, absolutely irresistible and the perfect way to use up a big bag of onions!