Preheat oven to 200 degrees Celsius Cut out four 4 1/2 inch rounds of puff pastry. Place on a baking tray and score in a lattice pattern across the top. Brush with beaten egg and bake 10-15 minutes until golden.
While pastry is cooking, heat 1 Tbsp oil in a skillet. Add mushrooms and stir-fry 2-4 minutes until softened. Season with salt and pepper and transfer to a plate. Add remaining oil to pan and cook half the steak. Stir fry 2-3 minutes and transfer to a plat, then repeat with other half of the steak.
Pour the gravy into the pan, stir in mushrooms and simmer 4-5 minutes. Add the meat to the skillet and cook another minute or two. add between 50-75 ml water.
Stir parsley into the sauce, divide mixture between four plates, and top each serving with a pastry 'lid'.
Delicious with boiled new potatoes and a green salad.