This is a rather superior tart and, although the mushrooms are expensive, I think the cost is justified by the deliciousness of the end result. I found girolles mushrooms but chanterelles or even cèpes (if you are lucky enough to source them) are great alternatives. It isn’t easy rolling out a piece of pastry to line a large tart tin so don’t despair if it breaks. You can patch up any gaps and, as the pastry is brushed with beaten egg before adding the filling, this helps to stop up any holes into which the filling might seep. A word about the tart tin; the tin I used is deeper than average so if you haven’t got a similar one you may find there is too much custard. It doesn’t matter but you will have a shallower tart. You could always use any leftover custard to make mini crustless quiches.
- For the parmesan pastry
- 250g plain flour
- pinch of salt
- 2-3 pinches mustard powder
- 125g cold unsalted butter, cut into rough cubes
- 40g finely grated parmesan
- 2 egg yolks
- 1 egg beaten
- For the filling
- 25g butter
- 2 leeks, trimmed, washed and finely sliced
- 400g girolles mushrooms or similar, brushed or washed and patted dry with kitchen roll if they are very dirty
- 2 tablespoons finely chopped tarragon
- 4 medium eggs
- 330ml double cream
- 100ml whole milk
- 40g finely grated parmesan
- For the pastry, place the flour, salt and mustard powder in a food processor and blend. Add the butter and blend until the mixture resembles fine breadcrumbs. Add the parmesan and pulse until just mixed in. Pour in the egg yolks and about 1-2 tablespoons cold water (start with 1 tablespoon) and pulse until the pastry starts to come together in large clumps. Turn out on to a floured board and bring together to form a smooth ball. Knead once or twice and flatten out slightly. Wrap in cling film and chill for 10 minutes.
- Heat the oven to 200˚c, fan oven 180˚c, mark 6. Roll out the pastry between two sheets of lightly floured baking parchment. The circle needs to be large enough to line a 28cm (11inch) metal, loose-bottomed tart tin. Drape the pastry over the tin and press to the edges, filling in any cracks with offcuts of pastry. Prick the base with the prongs of a fork and chill for 15 minutes.
- Place a scrunched up sheet of greaseproof paper over the pastry and pour in ceramic baking beans or pulses. Place on a baking tray and bake for about 20-25 minutes or until the sides of the pastry are golden and firm. Lift out the sheet of paper and baking beans and return to the oven for about 8-10 minutes. Brush the base and sides of the pastry with some of the beaten egg-this will help to keep the pastry crisp and the egg can seal any cracks. Return to the oven for 5 minutes. Remove and set aside. You can make the pastry case well in advance.
- For the filling, turn the heat down to 170˚c, fan oven 150˚c, mark 3. Melt the butter in a large frying pan and, stirring regularly, cook the leeks over a low heat for about 10 minutes until soft. Turn the heat up and add the mushrooms. Cook for 7-8 minutes until the mushrooms are soft and there is little or no liquid in the pan. Season with salt and ground black pepper. Tip the vegetables into a sieve and leave to drain for 5 minutes- just to ensure there is no excess moisture.
- Spread the leek and mushrooms over the pastry base and scatter over the tarragon. In a large jug beat together the eggs, cream and milk. Season with salt and pepper. Carefully pour into the pastry case- you can do this while the tart is on a rack in the oven. Sprinkle over the parmesan. Bake in the oven for 25-30 minutes or until the centre has stopped wobbling and the surface is golden.