Festive Veggie Pie

Name: Festive Veggie Pie
Prep time: 50 min
Cook time: 1 h 20 min
Total time: 2 h 10 min
Cuisine: European, British
Ingredients: 25 g butter; 450 g chestnut mushrooms; 2 thyme sprigs, leaves picked; 1 tsp. dried chilli flakes; 550 g butternut squash from the neck end, peeled; 1 tbsp. Dijon mustard; 125 g cranberry sauce; 200 g feta, crumbled, see intro; 100 g pistachio kernels, roughly chopped, see intro; 180 g cooked chestnuts, roughly chopped; Vegetable or olive oil, to grease; 675 g plain flour, plus extra to dust; 185 g unsalted butter, chopped; 1 medium egg, beaten