For the filling:
Heat a light drizzle of olive oil in a large frying pan.
Fry off the mince until golden brown and set aside.
In the same pan add a fresh drizzle of olive and sauté the mushrooms until golden brown and they have released all of their liquid. Season lightly and set aside with the mince.
Add a fresh drizzle of olive oil to the pan and sauté the onion and celery until soft.
Add the garlic, rosemary and dried herbs. Cook for a minute.
Add the tomato paste and cook until it turns a dark brick red colour.
Pour in the Worcestershire sauce and beef stock.
Add the mince and mushrooms back to the pan.
Bring everything to a simmer and cook until all the flavours have melded together.
Taste to adjust seasoning.
Remove from the heat and allow the filling to cool.
