1. Dice the beef into 2cm pieces and toss to coat in flour. Heat a large deep pan to a high heat and add 1 tablespoon of oil. Sear the beef in two batches. You may need to add a little more oil for each batch. Transfer to a plate and set aside.
2. In the same pan sauté finely chopped garlic until fragrant. Add sliced onion and cook until softened.
3. Add tomato paste, balsamic vinegar and cook for a further 2 minutes.
4. Return the seared beef to the pan and season generously with salt & pepper. Then add the beef stock, bay leaves and whole grain mustard. Bring to the boil, then transfer to a deep oven tray. Cover with a tight-fitting lid or foil then braise in the oven at 150°C for about 2 hours or until the meat is tender.
5. To thicken your pie mix make a slurry of equal parts cornflour and water, bring the mixture to the boil and slowly pour into the mixture until you get the desired consistency. Remove bay leaves. Allow the mixture to completely cool before using to fill your pie tins.
6. When you are ready to fill your pies, generously oil spray the pie tins. Cut pie bases and tops from the pastry and line your pie tins. Fill each base with the pie mix and top with a generous handful of mozzarella.
7. Place the pastry tops over the pies and crimp the edges to seal. Brush the tops with beaten eggs and sprinkle with cracked black pepper. Cut two small slits in the top of each pie.
8. Bake in the oven at 200°C for 25-30 minutes or until crisp and golden.
