In a food processor, add the plain flour and cold, cubed salted butter. Pulse until the mixture resembles fine breadcrumbs, about 30 seconds. Next, add the large egg and a splash of cold water, then pulse until a crumbly dough forms. Gather the dough into a ball, wrap it in cling film, and chill in the refrigerator for at least 1 hour.

Heat a frying pan over medium heat and add a drizzle of vegetable oil. Cook the diced bacon for about 4-5 minutes until crispy, then add the diced chicken thighs and stir-fry until the chicken is golden and cooked through, approximately 6-8 minutes.

In the same frying pan, add the finely diced onion, carrot, and celery. Sauté for about 7 minutes until softened and aromatic. Deglaze the pan by adding apple cider.

Sprinkle plain flour over the sautéed vegetables and stir to coat. Pour in the chicken stock and thickened cream while stirring continuously, bringing the mixture to a simmer to thicken.

Return the cooked chicken and bacon to the pan, stir to combine, and let the filling cool for about 15 minutes.

Preheat oven to 200°C (400°F). Roll out the chilled pastry dough, line a pie dish, pour the cooled filling into the pastry base, cover with top pastry, and seal the edges.

Transfer the pie to the oven and bake for 50-60 minutes, or until the pastry is puffed and golden brown. Let it cool slightly before slicing.