A classic onion tart is something everyone loves. And this slow-cooked caramelised onion tart made with four different types of onions is no exception. It is fantastically delicious. It’s also what I would all comfort food pure. It’s easy to make, inexpensive to prepare, filling and always better the next day. And best thing is everyone loves it.
Yellow onions, green onions, shallots and leeks are slow-cooked to bring out all their sweet amazing flavor. Crème fraîche, eggs, a pinch of nutmeg and fresh summer thyme are added to the mix and then baked in shortcrust pastry until golden brown, like a quiche but better. Life just got a little sweeter.
An onion tart is an absolute classic recipe
Depending on the region or country, onion tart is made with a yeast or shortcrust pastry and it’s prepared on a baking tray or in a round springform pan. It typically consists of onions, eggs, sour cream and smoked bacon, just like the the traditional German “Schwäbischer Zwiebelkuchen” which also has caraway seeds. Other regions use Schmand. And if you head over to France you find the “Französischer Zwiebelkuchen” which is made with fresh thyme, sardines and black olives. This version, after many variations, is my favourite by far. It may not be considered traditional in Germany, but this vegetarian version is definitely delicious.
Slow cooking the onions is key to this savory tart
You’ll note that the onions take what you might consider to be a long, long time to cook. Sweet, slow-cooked onions are exactly what make this vegetarian onion tart recipe a real treat. The process is easy and doesn’t take a ton of supervision. But the slow caramelisation process is exactly what makes this recipe so delicious. And to pass the time, how about listening to my personal playlist on Spotify: Chilled Out Kitchen Tunes.
How long does this vegetarian onion tart keep?
Covered in the fridge the onion tart can be enjoyed for 2-3 days. It is easily reheated and tastes just as good as leftovers. Which also means you can make this a day ahead if serving it for brunch.
Caramelised Onion Tart
- 3 small yellow onions, chopped
- 3 shallots, chopped
- 4 green onions, thinly sliced
- 3 small leeks, sliced
- 4 tablespoon butter
- 2 tbsp extra-virgin olive oil
- 3 large eggs
- 150 g container crème fraîche
- 1/4 tsp nutmeg
- 2 teaspoons fresh thyme leaves
- 1/2 tsp sea salt
- Freshly ground pepper, to taste
- 1 store-bought fresh quiche / tarte (Ø 32 cm / 300 g)
- Thinly sliced red onion rings to decorate (optional)
To serve (optional)
- 2 handfuls young arugula leaves
In a large deep sided skillet, melt 4 tablespoons of butter and 2 tablespoons oil. Reduce heat to moderately low and add onions, shallots, leeks and green onions.
Cover and cook for 10 minutes. Remove lid and continue to cook, stirring regularly, until the onion mixture is transparent, very soft and light golden color. This is a slow-cook method that takes about 30-40 minutes (read tips below!). Remove from heat and allow to cool for 10 minutes.
Meanwhile, preheat oven to 375°F / 190°C degrees and grease a large tart form with butter (I use a Ø 30 cm PYREX glass form).
In a large bowl, whisk together the eggs, crème fraîche, nutmeg, thyme, salt, and pepper. Add onion mixture and stir well combined.
Transfer the mixture to the pie crust and spread evenly with a spatula. If desired, garnish with a couple rings of thinly sliced red onion before baking. Bake for 35-40 minutes or until eggs are set and the crust is golden brown.
If desired, serve the tart with some young arugula leaves as a topping. Or make a simple side salad by tossing arugula with a little olive oil, lemon juice, grated parmesan, salt and pepper.
Tart can be made up to a day ahead. To warm up, cover and bake at 300°F / 150°C until warmed through.
Moderately low heat is around 2– 4 on the stove knob. Every stove operates differently, for mine I use setting 3, then setting 4 for the last 10-15 minutes. I use a large non-stick skillet which heats differently than a heavy bottomed one. A heavy-bottomed skillet retains more heat, cooks very evenly and is quicker in my experience. The main thing is, is to slow cook the onion mixture, without browning or burning them.
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