Preheat the oven to gas 4, 180ºC, fan 160ºC.
Put the flour into the bowl of a food processor and chop the butter into the flour in small pieces. Whizz quickly the mixture should look like breadcrumbs. Tip into a bowl, make a well in the middle and pour in the chilled water. Quickly, with cold hands, pull the flour into the water and pull into a ball of firm dough, do not ‘over work' it. Wrap the pastry in cling film and chill while you make the filling for the pie.
Heat the oil in a flat pan and add the peeled shallots. Fry gently for several minutes. Meanwhile, toss the skinned chicken thighs in the seasoned flour in a flat dish until they are well covered. Shake off any excess flour and add the chicken to the pan along with the halved mushrooms. Fry briskly until the chicken is lightly browned all over.
Put the cornflour into a bowl and gradually mix in the milk until you have a smooth paste. Then gradually add the stock and the wine. Add this mixture into the pan with the chicken, stirring well to get all the burnt bits off the bottom of the pan and then continuing to stir and cook gently until the sauce thickens. Season generously, then add the cream, stir in, taste and add further seasoning if it is needed. Turn the chicken mixture into a pie dish. If it does not fill the pie dish totally, put an egg cup or very small bowl in the middle to hold up the pastry and prevent it sinking into the filling.
Remove the pastry from the fridge and roll out between two pieces of floured clingfilm to prevent it cracking or sticking. Cut out the shape of your pie dish, generously. Use the trimmings to edge the pie dish, dampen the edge of the dish before laying on the pastry to make it stick. Then dampen the pastry rim. Using a rolling pin, roll the pastry off the counter and onto the top of your pie. Press down the edges with your finger, or a fork, and cut four slits to allow the steam to escape. Beat the egg in a bowl and then use a pastry brush to brush it over the top of your pie. Use any extra pastry trimmings to make leaves or pastry balls to decorate the top and brush them with egg too.
Bake in the centre of the oven for 50 minutes or until the pastry is cooked and lightly browned. Serve straight away with green vegetables and new potatoes.
Cook's tip: to save time, you can also purchase ready-made gluten-free pastry in some Tesco stores. Click here to sign in to Tesco groceries to see if it's available in your local store.
See more Gluten-free recipes