Marcus Wareing’s potato and tunworth cheesepot pie

Method

1. To make the pastry, rub the flour, butter and salt together in a mixing bowl with your fingertips until the mixture resembles breadcrumbs. (Alternatively, whizz briefly in a food processor.) Stir in the whole egg and 1 of the yolks and mix to form a soft dough. Shape into a ball, then flatten slightly into a disc. Wrap and chill for 30 minutes.
2. Dust a work surface lightly with flour, unwrap the pastry and roll it out into a 4 5mm thick circle slightly larger than the dish/tin. Transfer it to a tray and chill to rest again. The resting is important, as the pastry will relax and shrink back to its natural size.
3. Put the sliced potatoes in a saucepan, cover with water and add a pinch of salt, then bring to the boil over a medium heat. Once boiling, reduce the heat to a low simmer and cook for 5-8 minutes or until a knife can go through the slices but they’re still firm. Carefully drain the potatoes in a colander and allow to steam until really dry – any excess water will dilute the sauce.
4. Heat the oil in a separate frying pan over a low heat, add the shallots and garlic and fry for 8-10 minutes until translucent. Add the cubed cheese and salt, then cook over a low heat for a further 10 minutes until the cheese melts completely. Keep stirring the mixture to avoid it sticking to the pan.
5. Meanwhile, in a separate saucepan, heat the milk, cream and thyme until simmering (not boiling). Pour over the melted cheese mixture and stir until fully incorporated – it should resemble a rich cheese sauce. If the sauce is thin,  simmer it for 2-3 minutes to thicken it.
6. Heat the oven to 170°C fan/ gas 5. Put a layer of sliced potatoes in the baking dish/tin and season, then add a generous layer of the cheese mixture. Repeat the layers using the rest of the cheese and potatoes. Brush the edge of the dish with a little of the remaining egg yolk. Remove the rolled-out pastry from the fridge and lay it on top of the dish, allowing it to hang over the top. Neaten the edges, leaving a slight overhang as it will shrink a little as it cooks, then glaze the pastry with the remaining egg yolk and sprinkle over the thyme leaves.
7. Bake in the oven for 30-35 minutes until the pastry is golden brown. Remove from the oven, sprinkle with sea salt flakes and serve immediately with a crisp green salad.