A crustless onion tart skips the yeast dough entirely. The egg, soured cream and cheese mixture binds the 800 g of steamed onions so firmly that every slice holds its shape, even without a traditional base underneath.
We have been making this crustless onion tart for years, every time the new-season wine appears in the shops and nobody wants to spend an hour waiting for a yeast dough to prove. The eggs combined with soured cream and 300 g of Emmental are our entire binding agent. The cheese melts and threads through the onions as it bakes, acting like a net around them rather than just sitting on top as a topping.
The practical bonus: we end up with significantly fewer carbohydrates than in the classic Thermomix® onion tart with a pastry base. If you want to cut out flour altogether, leave out the 130 g of flour and replace it with 50 g of ground almonds. The set will be a little softer, but firm enough for clean slices.
Crustless Onion Tart with the Thermomix®
Ingredients 0 / 10 ✓
- 300 g Emmental
- 800 g onions
- 50 g clarified butter
- 250 g bacon lardons
- 130 g flour
- 300 g soured cream
- 5 eggs
- 1 tsp caraway seeds
- 1 tsp salt
- 1/2 tsp white pepper
Instructions 0 / 5
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1
Chop the cheese.
Preheat the oven to 180°C top and bottom heat and grease a springform tin. Place the Emmental in pieces into the mixing bowl, chop for 10 seconds / speed 8 and set aside.
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2
Chop the onions.
Peel and halve the onions. Place one half of the onions into the mixing bowl, chop for 5 seconds / speed 4 and set aside. Place the second half of the onions into the mixing bowl, chop for 5 seconds / speed 4 and push down with the spatula.
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3
Sweat the bacon and onions.
Add the clarified butter and bacon lardons, mix for 10 seconds / reverse direction / speed 3, then cook for 10 minutes / Varoma / reverse direction / speed 2 without the measuring cup.
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4
Mix the batter and bake.
Add the flour, soured cream, eggs, cheese, caraway seeds, salt and pepper and mix for 15 seconds / reverse direction / speed 4. Transfer the onion mixture into the prepared springform tin and bake on the middle shelf of the oven for approximately 40 to 45 minutes.
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5
Rest and serve.
Leave the onion tart to rest for 5 to 10 minutes before slicing and serving.
Tip: You can leave out the bacon lardons and add freshly chopped herbs instead.
Video
Nutrition per serving
What holds this crustless onion tart together
5 eggs to 300 g soured cream plus flour as a binder. That is the ratio that works. Fewer eggs and the mixture collapses as soon as you release the springform. More soured cream and the tart stays too wet and will not cut cleanly.
Chop the onions roughly, never blend them to a puree. In the Thermomix® we go to 5 seconds / speed 4, and we do it in two batches. All 800 g of onions at once get chopped too finely in the mixing bowl, because the bottom layers are right next to the blade and turn to mush while the top layers are still in chunks. Halve the quantity, chop in two rounds, and everything stays nicely coarse.
Cook the bacon and onions together for 10 minutes at Varoma. This is the step where many people give up too early. Pulling them out after 5 minutes means watery onions in the tin. At a full 10 minutes on Varoma / reverse direction / speed 2 without the measuring cup, enough liquid evaporates so the egg and soured cream mixture is not too runny afterwards. Without the measuring cup means: steam escapes rather than dripping back into the bowl.
Where a crustless onion tart goes watery or rubbery
Watery base in the tin
If there is still a puddle under the tart after 45 minutes, it almost always comes down to onions that were not cooked long enough. Our fix: cook without the measuring cup the whole time and go the full 10 minutes. We check before mixing with eggs and soured cream that the onion mixture is translucent and no longer looks wet.
Cheese settles on top
If the Emmental forms a crust on top and the rest of the tart looks cheese-free, it was not mixed in properly. Our fix: the chopped cheese goes into the mixing bowl together with the flour, soured cream and eggs for 15 seconds / reverse direction / speed 4. The reverse direction stirs without chopping the cheese further. It stays in small pieces throughout the mixture rather than melting into a layer on top.
Tart falls apart when sliced
Slicing or turning out a tart straight from the oven never ends well. The egg and soured cream binding needs time to set. Our fix: leave it to rest in the tin for 5 to 10 minutes, then run a thin knife around the edge and only then open the springform ring. Cutting while the tart is still piping hot gives you crumbles rather than clean slices.
Bacon stays soft instead of crispy
250 g of bacon lardons in the mixing bowl will go soft on Varoma but rarely turn properly crispy. That is down to how the bowl works, because there is little direct browning in an enclosed container. Our fix: if you want crispy bacon on top, fry an extra 50 g briefly in a pan and scatter it over the tart in the last 10 minutes of baking. The 250 g cooked in the mixing bowl still release their full flavour into the mixture.
With bacon, vegetarian or as a quiche-style variation
Vegetarian without bacon: We leave out the 250 g of bacon lardons and add 200 g of smoked tofu cut into small cubes. It brings a similar smoky note without making the tart watery.
With leek instead of just onions: 500 g onions plus 300 g leek cut into rings gives a milder result. Add the leek only in the last 5 minutes of the cooking time so it does not fall apart.
On a baking tray instead of a springform tin: Spreading the whole mixture onto a baking tray lined with baking paper gives a flammkuchen-style look. You only need 30 minutes in the oven because the layer is thinner.
Low-carb version: Leave out the flour entirely and use 60 g ground almonds and an extra tablespoon of soured cream instead. That brings us down to around 6 g of carbohydrates per slice, compared to around 30 g in the classic onion tart.
With mountain cheese instead of Emmental: 300 g of a strong mountain cheese makes the tart more robust and pairs better with a full-bodied wine. Emmental is milder and more family-friendly.
What we serve alongside
Classically we drink new-season wine alongside, while it is in season. The lightly sparkling, slightly sweet profile cuts through the richness of the cheese and bacon. Outside of new-wine season, a light Riesling or a dry still cider works well. As a side, a simple green salad with mustard vinaigrette is all you need.
If you are planning a full autumn evening, combine this crustless onion tart with a classic onion tart with yeast pastry on a buffet, add an all-in-one vegetable and soured cream pot, and finish with a sweet potato gratin as a second warm course. We also have a quiche-style variation without classic shortcrust pastry.
Keeps for 3 days in the fridge, warm up briefly in the oven
Stored in an airtight container, the crustless onion tart keeps well in the fridge for 3 days. Many people find it even better on the second day, once the onion and bacon flavours have had time to meld with the cheese.
Reheating works best in the oven at 160°C top and bottom heat for 12 to 15 minutes. The microwave makes the binding rubbery and the cheese tough, so we avoid it. You can also freeze it: pre-freeze individual slices on a board, then transfer to freezer bags. It keeps for up to 3 months. Defrost overnight in the fridge, then reheat in the oven as if fresh.
How other recipes approach it
We looked at three popular versions. One blog fries the onions and bacon in a pan on purpose, because that brings more browning than the mixing bowl alone, but uses only 100 g soured cream to 4 eggs. Another works entirely in the Thermomix® with 120 g cream and 3 eggs and treats caraway as optional. A third goes for a low-carb take with 150 ml milk instead of soured cream, 5 eggs and only 150 g bacon lardons. Our recipe stays with soured cream for a rich egg and cheese binding, keeps the caraway as the classic flavouring note, and mixes the onions completely in the bowl so that one appliance does the whole job.
More hearty classics with the Thermomix®:
- Onion tart with yeast pastry
- Pizza dough with the Thermomix®
- All-in-one vegetable and soured cream pot
- Gnocchi bake
- Sweet potato gratin
