Heat half the oil in a large frying pan over high heat. Add the onion and cook, stirring, for 5 minutes or until soft.
Add the beef and pork mince and cook, stirring with a wooden spoon to break up any lumps, for 5 minutes or until mince changes colour.
Add the tomato paste and cook, stirring, for 1 minute or until heated through. Add the tomatoes and stock, and bring to the boil.
Reduce heat to low and cook, stirring occasionally, for 45 minutes or until sauce thickens. Remove from heat and set aside for 30 minutes to cool.
Meanwhile, cook the pasta in a large saucepan of salted boiling water following packet directions or until al dente. Drain well. Set aside to cool.
Heat a large non-stick frying pan over medium-high heat. Add the bacon and cook, stirring, for 5 minutes or until crisp. Use a slotted spoon to transfer to a plate lined with kitchen paper.
Add the remaining oil to the pan. Add half the chicken livers and cook for 2 minutes each side or until golden. Transfer to a plate lined with paper towel. Repeat with remaining chicken livers.
Preheat the oven to 180 C / Gas 4.
Combine the mince mixture, pasta, the 3 eggs and Parmesan in a large bowl. Mash the ricotta in the milk and add to the mixture.
Add the bacon and hard-boiled eggs and gently fold until just combined. Taste and season with salt and pepper.
Line the base and side of a round 23cm (base measurement) cake pan with 2 of the pastry sheets. Trim excess pastry.
Spoon half the pasta mixture over the pastry base. Top with chicken livers. Spoon the remaining pasta mixture over the chicken livers and smooth the surface.
Top with the remaining pastry and lightly press the edges to seal. Brush with the extra egg.
Bake in preheated oven, covering with foil if pastry browns too quickly, for 1 hour or until golden brown.
Turn timpana onto a baking tray and bake for a further 15 minutes or until golden.
Remove from oven. Set aside for 20 minutes to cool slightly. Cut into wedges and serve with mixed salad leaves, if desired.