Preheat the oven to 180°C conventional oven/ 160°C fan-forced (350° Fahrenheit/Gas 4). Line a large baking tray with baking paper.
Place 4 of the eggs in a small saucepan and cook, covered completely with water, over high heat. Bring to the boil, then cook for a further 5 minutes. Carefully tip out the boiling water from the saucepan and fill with cold water to cool the eggs. Once cool, peel the eggs (leaving them whole).
Heat the canola oil in a non-stick frying pan over medium heat. Add red onion and cook, stirring, until the onion is soft (approximately 4 minutes). Set the frying pan aside for the onion to cool.
Place the breadcrumbs in a large bowl and pour the milk over to soak for a few minutes. Break up the sausage meat with your hands and add it to the bowl with milk-soaked breadcrumbs. Add the lamb mince (ground meat), remaining 2 eggs (raw), Pecorino, rosemary, thyme and chopped ham. Season with salt, then use your hands (or you may wish to use disposable gloves), to mix until well combined.
Place a large rectangular piece of baking paper on a clean work surface. Spoon the meat mixture onto the baking sheet. Use a metal spoon to press the meat mixture into a large rectangle shape that is approximately 24cm x 28cm in size. Arrange the peeled eggs in one long row in the centre of the meat mixture, allowing 2cm from the edges.
Use the baking paper to roll the polpettone (meatloaf) from the short end to enclose the egg filling. Smooth the middle joint and ends of the rolled meat mixture. Remove the baking paper and transfer the polpettone to the prepared baking tray (it is easiest to roll it onto the tray). Rub olive oil all over the polpettone. Pour over the hot vegetable stock and place 2 knobs of butter on top. Bake for 45 minutes or until the polpettone is browned and cooked through.
Allow polpettone to cool for 10 minutes before slicing to serve – buon appetito.
500g lamb mince (ground meat)|250g lamb and rosemary sausages, skin removed|6 eggs|2 tablespoons canola oil|½ red onion, finely chopped|30g dried breadcrumbs|70ml milk|30g Pecorino cheese, finely grated|2 sprigs rosemary, finely chopped|1 sprig thyme, finely chopped|100g thinly sliced ham, finely chopped|3 tablespoons extra virgin olive oil|125ml hot vegetable stock|2 knobs butter|Sea salt