Preheat oven to 200°C (or 180°C fan bake).
Heat a drizzle of oil in a large fry pan on medium heat. Cook beef mince, stirring, for 5 minutes, until browned. Add gravy mix and water measure and stir to combine. Reduce to low heat and cook for 2-4 minutes, until reduced and thick. Remove from heat.
Meanwhile, roll out pastry. Use a small cup or cookie cutter to cut out circles from pastry. You will need 24 circles total for the bottom and top of each pie (you may need to re-roll the pastry to get all the circles). Grease a muffin tin and place a pastry circle into each muffin cup.
Stir cheese into beef mixture and fill the pastry cups with mince mixture. Place a pastry lid on top. Use a fork to crimp together the edges of the pastry.
Whisk an egg and brush over top of pies. Bake in oven for about 20-25 minutes, until puffed and golden.
Plate up pie with tomato sauce.