300g mozzarella (grated or pre-sliced - not fresh)
1 egg, beaten
Preheat the oven to 190*C.
Preheat a large heavy based casserole dish. Brown the mince on all sides - this will take 2-3 minutes. You may need to do it in batches depending on the size of your pan as if you overcrowd it the meat will sweat instead of browning. Remove the meat and set aside.
Turn down the heat and render the smoked pancetta, until beginning to turn golden brown. Add the onion and sweat for 10-12 minutes until very soft and starting to turn golden brown. Add the garlic cloves and cook for a further minute. Add the tomato puree and cook for a minute more. Add the chopped tomatoes, red wine, beef stock and bay leaf. Bring to the boil then reduce to a bare simmer and cook, partially covered for around an hour and a half until the sauce is beautifully reduced and flavourful and the meat is tender. Season to taste, adding marmite if you think the sauce needs more depth of flavour.
Unroll the pre-rolled pastry sheet, and cut into four squares. Spoon a layer of bolognese into each of the pie dishes, followed by a layer of mozzarella. Cover this with another layer of bolognese, then cover with one of the puff pastry squares. Trim off the excess, use a fork to crimp along the edges, and make a slit in the middle to allow steam to escape. Brush with the egg wash and bake for 10-12 minutes until the pastry is golden brown.