Porcini are one of the most prized mushrooms. They are dried for preservation and when rehydrated in water they bestow their powerful, almost meaty flavour to the liquid. This tart uses that liquid and other mushrooms, as well as the porcini themselves, so it is crammed with mushroom flavour.
- for the shortcrust pastry:
- 200 g plain flour, sifted
- 100 g chilled butter (cubed, plus extra for greasing)
- 1/2-1 egg (beaten)
- for the filling:
- 15 g butter
- 200 g button or large flat mushrooms (finely chopped)
- salt and ground black pepper
- 25 g dried mushrooms (such as porcini)
- 250 ml boiling water
- 2 eggs
- 1 egg yolk
- 250 ml double or regular cream
- 100 g shallots (peeled and finely chopped)
- for the tarragon hollandaise:
- 3 egg yolks
- 175 g butter (diced)
- squeeze of lemon juice
- 1/4 tsp dijon mustard
- 3 tblsp chopped tarragon
- 23cm (9") diameter loose-bottomed tart tin
- Place the flour and butter in a food processor and whiz briefly until the butter is in small lumps. Add half the beaten egg and continue to whiz for another few seconds or until the mixture looks as though it may just come together when pressed. (Prolonged processing will only toughen the pastry, so don't whiz it up until it is a ball of dough.) You might need to add a little more egg, but not too much as the mixture should be just moist enough to come together. If making by hand, rub the butter into the flour until it resembles coarse breadcrumbs then, using your hands, add just enough egg to bring it together. Reserve any leftover egg to use later.
- With your hands, flatten out the ball of dough until it is about 2cm (3/4 in) thick, then wrap in cling film or a plastic bag and leave in the fridge for at least 30 minutes.
- When you are ready to roll out the pastry, butter the tart tin and remove the pastry from the fridge, placing it between two sheets of cling film (each larger in size than your tart tin). Using a rolling pin, roll the pastry out to no thicker than 5mm (1/4 in). Make sure to keep it in a round shape as well as large enough to line both the base and the sides of the tin.
- Remove the top layer of cling film, slide your hand, palm upwards, under the bottom layer of cling film, then flip the pastry over (so that the cling film is now on top) and carefully lower it into the tart tin. Press the pastry into the edges of the tin (with the cling film still attached) and, using your thumb, 'cut' the pastry along the edge of the tin for a neat finish. Remove the cling film, prick over the base with a fork and chill the pastry in the fridge for another 30 minutes or in the freezer for 10 minutes (it can keep for weeks like this in the freezer).
- Preheat the oven to 180°C (350°F/Gas 4).
- Remove the pastry from the fridge and line with foil, greaseproof paper or baking parchment, leaving plenty over the sides. Fill with baking beans or dried pulses (all of which can be reused repeatedly), then place in the oven and bake 'blind' for 15-20 minutes or until the pastry feels dry in the base. Take out of the oven, remove the baking beans and foil/paper, brush the base of the pastry with any leftover beaten egg, then bake for another 3 minutes or until lightly golden. Remove from the oven and set aside.
- Next make the filling. Melt the butter in a large frying pan on a medium heat, add the shallots, cover with a lid and cook for 7-8 minutes or until soft but not browned. Stir in the mushrooms, season with salt and pepper and cook, uncovered, for 8-10 minutes or until soft and dark and any juices that have come out during cooking have evaporated.
- While these are cooking, soak the dried mushrooms in the boiling water for 10 minutes. Drain, reserving the soaking liquid, then finely chop the soaked mushrooms and add to the shallot and mushroom mixture along with the soaking liquid. Continue to cook, stirring occasionally, for about 10 minutes or until the liquid has completely evaporated. Remove from the heat and allow to cool for a few minutes.
- Meanwhile, whisk together the eggs, egg yolk and cream, then add to the mushrooms. Mix together and then pour into the pre-baked tart case. Place in the oven and cook for about 30 minutes or until the filling has completely set.
- While the tart is baking make the Tarragon Hollandaise, stirring the mustard and tarragon into the cooked sauce just before seasoning.
- For the Tarragon Hollandaise:
- Place a heatproof bowl over a saucepan of simmering water on a medium heat. (The water must not boil. If it does it may heat the sauce so much that it will scramble or curdle - so take the pan off the heat every so often.)
- Add the egg yolk and 1 tablespoon of cold water and whisk together.
- Gradually add the butter, a few bits at a time, until each addition has melted and emulsified as it is whisked in, before adding the next.
- Once all the butter has been incorporated, cook for a couple of minutes more, stirring constantly, until the sauce has thickened enough to coat the back of a spoon. Stir the mustard and tarragon into the cooked sauce just before seasoning
- Remove from the heat, and keep warm if necessary by covering with cling film and leaving to sit over the warm water, until you're ready to serve.
- Remove the tart from the oven, cut into slices while warm and serve with a generous drizzle of the Tarragon Hollandaise.
This recipe and many more are available in Rachel's book, 'Rachel Allen: Entertaining at Home', published by Harper Collins.
More by Rachel Allen:
- Milk Ice Cream: A little DIY, A lot of Taste
- Chocolate Meringue Cake: A serious picnic bonus
- Fennel, pink grapefruit, feta salad: Rachel Allen