Winter Chicken-Mushroom Pie

How to make a winter chicken-mushroom pie?

1. Make the pastry: mix 250 g flour with a pinch of salt in a bowl. Add 125 g cold butter in cubes and rub it into the flour with your fingertips until the mixture resembles coarse sand. Add 3 to 4 tablespoons of ice-cold water and knead briefly into a cohesive dough. Use as little water as possible, because too much makes the dough tough. Wrap it in plastic wrap and chill for 30 minutes in the refrigerator.
2. Preheat the oven to 200°C (top and bottom heat). Cut the chicken breasts into bite-sized pieces of about 2 cm. Heat the olive oil in a frying pan over medium heat and brown the chicken in 5 minutes. The chicken does not need to be fully cooked now, as it will finish cooking in the oven. Remove the chicken from the pan and set aside.
3. In the same pan, cook the onion and garlic over low heat until translucent, about 3 minutes. Add the chestnut mushrooms and shiitake and fry on high heat until all the liquid has evaporated, about 5 to 6 minutes. This is an important step: mushrooms hold a lot of water and if it doesn't evaporate fully, your filling will be too runny.
4. Sprinkle 2 tablespoons of flour over the mushroom mixture and stir well so the flour lightly coats the bottom of the pan. Add the chicken stock little by little while stirring to avoid lumps. Then pour in the heavy cream and bring the mixture to a simmer while stirring. Stir the chicken through, season with salt, pepper and thyme, and let the filling gently thicken for 5 minutes over low heat. Remove the pan from the heat and let the filling cool completely.
5. Take the dough out of the fridge. Lightly dust your work surface with flour and roll out two-thirds of the dough into a round sheet slightly larger than your quiche pan. Lightly grease the pan with butter and line the bottom and sides carefully with the dough. Press it well into the corners so there is no air underneath.
6. Spoon the cooled filling into the pastry-lined pan and spread evenly. Roll out the remaining dough into a round sheet for the lid and place it over the filling. Press the edges firmly together and trim off excess dough with a knife. Make four small slits in the centre of the lid with a sharp knife so steam can escape during baking. That prevents the pastry from puffing up and cracking.
7. Brush the top of the pie with the beaten egg. This gives the crust its glossy, golden-brown colour. Put the pie in the preheated oven and bake for 35 to 40 minutes at 200°C, until the crust is golden and feels crisp.
8. Remove the pie from the oven and let it rest for 10 minutes on the counter before slicing. The filling needs that time to set a little, otherwise everything will run when you cut it. Slice into wedges at the table and serve immediately.