Tarte a l'Oignon Caramelisee au Gruyere
A deeply golden tart of slowly caramelised onions and thyme in a creamy egg custard under a layer of nutty gruyere.
Made with Shortcrust pastry. Make a batch of the base first, then this takes minutes. Skip to the method
- Time1 hr 30
- LevelMedium
- Costabout £0.58 a head
- Oven200°C (180°C fan)
Cost is worked out from Aldi and Tesco shelf prices in October 2026. Your shop and brands will differ.
Ingredients
Tick what you need to buy. It goes on your shopping list.
Method
- 1
Melt the butter with the oil in a large, wide pan over a medium low heat. Add the onions with a pinch of salt and cook, stirring often, for 35 to 40 minutes until very soft and deep golden. Add the thyme and vinegar for the last 2 minutes.
40 min - 2
Meanwhile, heat the oven to 200°C (180°C fan). Roll out your ready made shortcrust pastry (see the base recipe) and line a 25 cm loose bottomed tart tin. Chill for 20 minutes, then blind bake with paper and beans for 15 minutes. Remove them and bake for 5 minutes more. Lower the oven to 180°C (160°C fan).
20 min - 3
Whisk the eggs, cream and milk with pepper and a grating of nutmeg if you have it.
- 4
Spread the cooled onions in the pastry case, pour in the custard and scatter with the gruyere.
- 5
Bake for 30 to 35 minutes until just set and golden. Rest for 10 minutes before slicing.
33 min 20 s
Tips
- Be patient with the onions. Slow, steady cooking brings out natural sweetness, and rushing leaves them pale or burnt.
- Add a splash of water to the pan if the onions start to catch.
- Let the onions cool before adding the custard or the eggs can scramble.
Storing and freezing
Cool within 2 hours and keep in the fridge for up to 3 days. Serve cold or reheat slices at 160C (fan 140C) for 12 minutes until hot through. Not suitable for freezing.
Questions
How many onions do I need?
About 900 g raw, or around 6 medium onions. They cook down to roughly a third of their volume.
Can I use a different cheese?
Yes. Comte, mature cheddar or Emmental work well. Use 80 g and keep a strong, nutty flavour.
Is it the same as an Alsace tarte a l'oignon?
They are similar. The Alsace version often uses bacon, but this vegetarian one keeps the creamy custard and sweet onions.
More made with shortcrust pastry
Double check before you cook. Recipes can contain mistakes. Any diet labels come from the ingredients as written in this recipe and are a guide, not a guarantee. Always check every ingredient and the packet label for allergens and cross contamination, and ask your doctor or dietitian what is right for you, especially with coeliac disease, diabetes or a serious allergy. This is not medical advice.