Recipes › Leek › Leek, Gruyère and Mustard Tart
Leek, Gruyère and Mustard Tart
A buttery shortcrust case filled with slow-cooked leeks, sharp Gruyère and a Dijon-spiked custard. This is the sort of tart you find on a French market stall — unpretentious, deeply savoury and genuinely satisfying. It works equally well warm from the oven or at room temperature, which makes it ideal for a winter lunch with dressed leaves.
Leek is usually ready October to February. More leek recipes, or see what to sow this month where you are.
Ingredients
- 800 g Leeks, trimmed, halved lengthways, sliced into 1cm half-moons, washed
- 200 g Plain flour
- 100 g Cold unsalted butter, cut into 1cm cubes
- 35 ml Cold water
- 30 g Unsalted butter
- 120 Gruyère, coarsely gratedor use Comté or a good mature Cheddar
- 200 ml Double cream
- 3 Whole eggs, lightly beaten
- 2 tbsp Dijon mustard
- 1 tsp Fresh thyme leaves, picked
- 1 tsp Fine sea salt
- 1 pinch Freshly ground black pepper
- 1 pinch Freshly grated nutmeg
Contains: cereals gluten, eggs, milk, mustard.
Method
- Make the pastry. Put the flour and a pinch of salt into a large bowl. Add the cold cubed butter and rub it in with your fingertips until the mixture resembles coarse breadcrumbs with a few pea-sized lumps remaining. Add the cold water one tablespoon at a time, mixing with a knife until the dough just comes together. Do not overwork it. Shape into a disc, wrap and refrigerate for 30 minutes.About 10 min
- While the pastry chills, melt the 30g butter in a wide frying pan over a medium-low heat. Add the leeks, thyme and a good pinch of salt. Cook, stirring occasionally, for 15 minutes until the leeks are very soft, sweet and almost jammy. If any liquid releases, keep cooking until it evaporates. Remove from the heat and leave to cool.About 17 min
- Preheat your oven to 190°C fan. On a lightly floured surface, roll the pastry out to about 3mm thick and use it to line a 23cm loose-bottomed tart tin. Press it firmly into the edges, letting any excess hang over the rim. Prick the base all over with a fork, line with baking parchment and fill with baking beans or uncooked rice. Blind bake for 15 minutes.About 18 min
- Remove the baking beans and parchment. Return the pastry case to the oven for a further 5 minutes until the base looks dry and just beginning to turn golden. Remove and trim off the overhanging pastry with a sharp knife. Reduce the oven temperature to 170°C fan.About 6 min
- Whisk together the double cream, beaten eggs, Dijon mustard, nutmeg, a pinch of salt and a generous grind of black pepper in a jug until smooth.About 2 min
- Spread the Dijon mustard evenly over the base of the warm pastry case. Spoon in the cooled leeks, spreading them into an even layer. Scatter over three-quarters of the Gruyère. Pour the cream and egg custard over the top slowly and evenly, then scatter the remaining cheese over the surface.About 3 min
- Carefully transfer the tart to the oven and bake for 30 to 35 minutes, until the custard is just set with a very slight wobble in the centre and the top is golden. Leave to rest in the tin for 10 minutes before slicing.About 35 min
Tips
- Really cook the leeks down — they should be sweet and concentrated, not watery. Wet leeks will make the custard fail to set properly and the base will go soggy.
- Spreading a thin layer of Dijon directly on the pastry before adding the filling creates a subtle mustard hit in every bite and also helps keep the pastry crisp by acting as a moisture barrier.
- The tart is best eaten the day it is made, but if you are baking ahead, reheat slices at 160°C fan for 8 minutes — it brings the custard back to life beautifully.
Ring the changes
- Add 100g of diced smoked bacon or lardons, fried until crisp, to the leek layer for a more substantial, meat-lover's version.
- Swap the Gruyère for a good blue cheese such as Fourme d'Ambert for a sharper, more intense flavour.
Keeping it
Store any leftover tart covered in the fridge for up to 2 days. Reheat at 160°C fan for 8 to 10 minutes. Not suitable for freezing once the custard is set.
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