1. Preheat the oven to 180°C
2. Heat the oil in a saucepan on moderate heat and gently saute the onion, garlic and mushrooms
3. Mix the mustard powder and flour, and use the mix to coat your pork cubes
4. Add the pork cubes to the pan and saute until golden brown
5. Add the fresh sage, sherry, and vegetable stock and cook for 20 minutes on moderate heat
6. Meanwhile, roll out the pastry on an excellent surface and use a rolling pin to smooth the dough evenly
7. Divide the pork filling in half and place each halved amount in the middle of each prepared pastry
8. Close the pastry around the filling and pinch the sides together to contain the filling
9. Place the filled pastry rolls onto a baking tray, brush with the beaten egg, and bake for 20mins or until golden brown