Onion Tart
Slowly cooked onions with thyme and cream in a shortcrust case, cooked for 30 minutes until set and golden.
Before You Start
Cook the onions slowly.
Blind bake the case.
If your oven runs hot, check at 24 minutes.
Cool before slicing.
Making Onion Tart
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Melt the butter and cook the onions with the salt over low heat for 30 minutes, stirring now and then, until deep gold. Cool.
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Heat the oven to 200°C / 390°F. Line a 23 cm tin with the pastry and cook blind for 15 minutes, then 5 minutes without beans. Lower the oven to 180°C / 355°F.
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Whisk the eggs, cream, thyme leaves and pepper. Stir in the onions and pour into the case. Scatter with the gruyere.
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Cook for 30 minutes until set with a slight wobble. Cool for 10 minutes.
What's Going On Here
The onions are the filling and they take longer than anything else. Cooked slowly in butter they turn sweet, soft and golden, and with an egg and cream custard they make a tart that is much more than the sum of its parts.
Slice the onions thinly and cook them over low heat for 30 minutes, stirring now and then, until they have collapsed and are a deep gold. Do not rush with high heat, because browned onions are bitter and burnt ones are worse. A pinch of salt helps them release their water.
Blind bake the case for 15 minutes with beans, then 5 without, so that it is dry and will not turn soft under the filling.
Mix the eggs, cream and thyme, fold in the cooled onions and pour into the case. Cook at 180°C for 30 minutes, until set with a slight wobble. If your oven runs hot, check at 24 minutes. Cool for 10 minutes before slicing.
Leftovers, Reheating and Keeping
Keeps in the fridge for 3 days. Good cold or warmed gently.
If You're Missing Something
- Double cream won't whip if you swap it, but for the cooking itself, full-fat crème fraîche or a lower-fat single cream works in its place.
Good With
- Green salad
- Cold ham
- Dijon vinaigrette
- White wine
Still Wondering?
How long does Onion Tart take to make?
About 1 hour in total — 20 minutes of preparation and 40 minutes of cooking. The recipe serves 6.
What are the key tips for making Onion Tart?
Cook the onions slowly. Blind bake the case. If your oven runs hot, check at 24 minutes. Cool before slicing.
What should I serve with Onion Tart?
Green salad; Cold ham; Dijon vinaigrette; White wine.
How should Onion Tart be stored?
Keeps in the fridge for 3 days. Good cold or warmed gently.
Is Onion Tart suitable for a special diet?
This recipe is vegetarian and no added sugar. Those labels are checked against the ingredient list, so a dish is only marked when nothing in it contradicts the claim.
How many calories are in Onion Tart?
About 546 kcal per serving, with 11 g protein, 40 g carbohydrate and 38 g fat. The figures are calculated from the ingredient list and are an estimate.
Onion Tart Nutrition Facts
Per serving, calculated from the ingredient list. Treat these as an estimate — brands and cuts vary.
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Written and tested by Turab
One person, one kitchen — no test kitchen, no team. How every recipe on this site is checked before it goes up.
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