Season the steak with salt and pepper. Coat in flour, shaking off excess. Reserve leftover flour.
Heat the oil in a large frying pan over medium to high heat. Cook beef until nicely browned, then set aside. Add onion and mushrooms; cook, stirring until mushrooms are tender and liquid from them has evaporated. Stir in garlic and reserved flour. Cook for 2 minutes, stirring well.
Slowly add the stock constantly mixing to ensure you don’t get lumps of cooked flour. Add wine, thyme and steak and simmer for 5 mins. Season with salt and pepper; remove from heat, cool to room temperature and refrigerate until well chilled.
Preheat oven to 220 degrees C .
Place one sheet of pastry in the bottom of a 23cm pie dish. Fill with beef and mushroom mixture before topping with second layer of pastry.
Brush edges with egg wash and crimp to seal. Brush the top of the pie with egg wash. Cut a small hole in centre of pie to allow steam to escape.
Bake for 20 mins. Reduce the heat to 180 degrees C and cook for a further 25 minutes.