Heat the olive oil in a wide frying pan and brown the beef in chunks, then set aside.
Fry the pancetta until crispy then add the onion and cook until soft and almost caramelised.
Pour in the red wine and reduce until it's almost all disappeared, then add the beef back in along with the passata and tomato puree. Stir and bring to a simmer then add the beef stock. Bring back to a simmer, season, then put on a lid and place in the oven and reduce in the oven for around 3 hours, until the beef is tender.
While all this is happening get your bechamel ready - you presumably know the drill by now, but if not then heat the butter until foaming then stir in the butter and cook for around twenty seconds, until biscuity. Gradually pour in the milk, whisking it into a smooth paste each time, until you have a silky sauce. Strain if you have any lumps.
Meanwhile, slice the bread and mix together butter, garlic and parsley. Season to taste. Brush the slices on both side then toast in the oven on trays.
When you are ready to serve, spread a layer of toasts and top with mozzarella and (hot) beef ragu. Repeat with remaining toasts and sauce then pour over the bechamel. Scatter with parmesan and pop back in the oven for a bit to melt the mozzarella. Scatter with basil.