Substitute goulash with beef chuck or boneless shin.
Heat a tablespoon or two of olive oil over a high heat in a large saucepan. Add the beef in batches and sauté in the hot oil until brown. Remove the goulash from the saucepan and set aside.
Add the leeks and carrots to the saucepan and cook on a medium heat until softened. Add the garlic and sauté for an additional minute.
Add the remaining ‘stew’ ingredients, including the beef and its juices: beef stock, tinned tomatoes, wholegrain mustard, mustard powder, balsamic vinegar, tomato paste, potatoes, rosemary and bay leaves. Season generously with salt and pepper, stir to combine and bring to the boil.
Cover and simmer on low for about 1 hour or until the vegetables are cooked through and the beef is tender. Check every now and again to ensure it doesn’t catch and that there is enough liquid in the pot. Add a cup of water if necessary, you don't want the mixture to dry out.
Pre-heat the oven to 200°C/390°F.
Discard the bay leaves and rosemary sprigs and divide the beef ‘stew’ between 6 ramekins or 1 large pie dish.
On a lightly floured surface, using a rolling pin, roll out the puff pastry into a large rectangle. If you are using individual dishes cut out circles about 2cm bigger than the ramekins and if you are using a large pie dish, use the pastry as is.
Place the pastry lids over the meat mixture and seal by lightly pushing the pastry down onto the edges of each dish with a fork. Use the fork again to poke a few small holes in the top of each pie to allow steam to escape.
Generously brush the egg wash onto the pies and bake for 20-30 minutes until the pastry is cooked through and golden.
Allow to cool for a few minutes before serving. The pie/s can be accompanied with a nice garden salad.