Mornay onion tart
In a shortcrust pastry base, a rather thick onion tart, where onions and lardons are deliciously bound with a Mornay sauce.
38 K 4.9/5 (28 reviews)414411
Last modified on: November 5th 2026
For 6 people, you will need:
- 1
300 g shortcrust pastry (pâte brisée) - 2
1 kg onion - 3
50 g butter - 4
150 g smoked pork belly (or thick cut streaky bacon) - 5
4 tablespoons vinegar - 6
300 g mornay sauce - 7
30 g grated cheese - Total weight: 1,890 grams
Times for this recipe
Preparation
1 hour 3 min.
Cooking
1 hour 15 min.
All in all
2 hours 18 min.
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Step by step recipe
Step 1 - ⌛ 20 min.
Roll out 300 g shortcrust pastry (pâte brisée) then line a 22 cm (9-inch) diameter high-sided baking tin, which you will have placed on a sheet of baking paper in a baking tray.
Leave any excess dough around the edges, then place in the fridge to set aside.
Leave any excess dough around the edges, then place in the fridge to set aside.
Step 2 - ⌛ 10 min.
Step 3 - ⌛ 3 min.
In a large saucepan over medium heat, melt 50 g butter, and when hot, add the onions.
Season with salt and stir well.
Cover for the first 5 minutes.
Season with salt and stir well.
Cover for the first 5 minutes.
Step 4 - ⌛ 10 min.
Leave to cook until the onions are tender, checking the salt seasoning as cooked onions tend to be a little sweet.
Step 5 - ⌛ 5 min.
Your onions should be fairly dry, with little or no cooking juices.
If this isn't the case, because they've given off a lot of water during cooking, drain them in a fine sieve.
Set aside.
If this isn't the case, because they've given off a lot of water during cooking, drain them in a fine sieve.
Set aside.
Step 6 - ⌛ 3 min.
Preheat oven to 200°C (390°F).
Cut 150 g smoked pork belly (or thick cut streaky bacon) into small pieces.
Cut 150 g smoked pork belly (or thick cut streaky bacon) into small pieces.
Step 7 - ⌛ 8 min.
Toast them, without adding fat, in a small frying pan over medium heat.
Step 8 - ⌛ 1 min.
When toasted to your liking, add 4 tablespoons vinegar, and stir until evaporated.
Step 9 - ⌛ 2 min.
It's not essential, but I recommend adding 2 or 3 spoonfuls of already-cooked onions to the pan at the end of cooking, then stirring well to capture all the flavor of the grilled bacon.
Step 10 - ⌛ 2 min.
Pour the lardons + onions into the remaining onions and mix well.
Step 11 - ⌛ 2 min.
Add 300 g mornay sauce and mix well.
Step 12 - ⌛ 20 min.
Take the pastry mould out of the fridge, cut the excess pastry around the edges of the mould, place a sheet of baking paper on the bottom and fill with ceramic balls (or similar).
Bake at 200°C (390°F) for 20 minutes.
Bake at 200°C (390°F) for 20 minutes.
Step 13 - ⌛ 5 min.
In the meantime, you can roll out the pastry scraps into small strips to decorate the tart.
Step 14 - ⌛ 1 min.
After 20 minutes, remove the baking tray from the oven...
Step 15 - ⌛ 5 min.
... and remove paper and beads.
Step 16 - ⌛ 2 min.
Fill the tart with the onion-lardon-Mornay mixture.
Step 17 - ⌛ 2 min.
If you have made some, place the pastry strips on top.
Step 18 - ⌛ 3 min.
Sprinkle with a little grated cheese.
Step 19 - ⌛ 30 min.
Bake for a further 30 minutes.
Step 20
Enjoy warm or hot, on its own or with a small green salad.
Remarks
If you find your onions a little too soft at the end of cooking, you can add a good glass of dry white wine.
If you don't have a Mornay sauce, use a Béchamel sauce to which you can add grated cheese to taste.
You'll notice that in this recipe, the onions are cooked without coloring, but if you prefer, you can caramelize them. In this case, increase the weight of onions to 1.5 kg, as they will reduce even more.
If you don't have a Mornay sauce, use a Béchamel sauce to which you can add grated cheese to taste.
You'll notice that in this recipe, the onions are cooked without coloring, but if you prefer, you can caramelize them. In this case, increase the weight of onions to 1.5 kg, as they will reduce even more.
Keeping: 1 or 2 days in the fridge, protected by cling film.
Source: Homemade.
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Nutritional information
| Proteins | Carbohydrates | Fats | Calories | Energy | |
|---|---|---|---|---|---|
| Per 100 g | 5 g RDI=7 % | 13 g RDI=5 % | 12 g RDI=17 % | 179 kcal RDI=9 % | 747 kJ RDI=9 % |
| Per person | 14 g RDI=22 % | 40 g RDI=15 % | 39 g RDI=53 % | 562 kcal RDI=28 % | 2,355 kJ RDI=28 % |
| Whole recipe | 86 g RDI=132 % | 240 g RDI=91 % | 231 g RDI=316 % | 3,374 kcal RDI=169 % | 14,128 kJ RDI=169 % |
How much will it cost?
For 6 people
5.40 €
Per person
0.90 €
Note: Be careful, these prices are only an estimate, you can consult the table of prices by ingredients used for this estimate.
This recipe uses (among others)
Onion
Like these other recipes:
Mornay Sauce
You can get more informations, or check-out other recipes which use it, for example:
Shortcrust pastry (pâte brisée)
You can get more informations, or check-out other recipes which use it, for example:
Smoked pork belly (or thick cut streaky bacon)
Like these other recipes:
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