Mushroom and potato dauphinois tarts

Method

1. Put the dried porcini mushrooms into a bowl and cover with freshly boiled water. Set aside to soak for at least 30 minutes. Lightly butter the two tartlet tins.
2. For the pastry, put the flour, oatmeal and a pinch of salt into a food processor with the 30g butter and whizz briefly until the mixture resembles fine breadcrumbs. Add the grated cheese and whizz again. Add 2 tsp cold water and process very briefly until the mixture comes together into a ball. Turn the pastry out onto a lightly floured surface and knead briefly until smooth, then cut in half. Roll each piece out to the thickness of a £1 coin and use to line the buttered tartlet tins. Press the pastry right into the edges of the tins, so it comes 0.5cm above the tops of the tins. Prick the bases here and there with a fork, then chill for 20 minutes.
3. Put a baking tray into the oven and preheat it to 200°C/fan180°C/gas 6. Line the pastry cases with foil, then fill with baking beans or rice, put them on the heated baking tray and bake for 15 minutes until the top edges are biscuit coloured. Remove the foil and beans/rice, then return the cases to the oven for a further 7-10 minutes until crisp and golden. Remove and set aside while you make the filling (see tip).
4. For the filling, melt 10g of the butter in a medium pan, add the onion, cover and cook over a low heat for 10 minutes until soft and lightly golden. Uncover, add the garlic and cook for 1 minute more. Cut the potatoes into 5mm thick slices, then add them to the pan with the milk, cream and some seasoning. Simmer gently for 15-20 minutes, stirring carefully every now and then until the potatoes are tender. (Be careful they don’t catch on the bottom of the pan.)
5. Meanwhile, drain the porcini mushrooms, squeeze out the excess water, then chop them quite finely. Heat the remaining butter in a frying pan, add the porcini and chestnut mushrooms and fry briskly for 3 minutes until tender and any excess liquid has evaporated but the mixture remains moist. Season lightly.
6. When the potatoes are tender, stir in half the grated cheese and season to taste. Spoon half the potato mixture into the bases of the tartlet cases, then cover with the mushroom mixture. Spoon the remaining potato mixture on top, then sprinkle with the rest of the grated cheese. Bake on the baking tray for 10-15 minutes until the tarts are golden and bubbling.