Preheat oven to 180˚C. Line 2 large baking trays with baking paper. Heat the oil in a large frying pan over a medium heat. Cook the onion, carrot, potato and garlic for 4-5 mins or until the onion mixture begins to soften. Add the fennel seeds, chilli flakes, if using, and salt. Cook for 1 min. Transfer to a large heatproof bowl and set aside for 15 mins to cool.
Add the ham, parsley, cranberries, tomato sauce, breadcrumbs and Worcestershire sauce to the onion mixture in the bowl. Stir until well combined. Add the sausage mince and stir until well combined.
Cut the pastry sheets in half crossways and place on a clean work surface. Divide the sausage mince mixture evenly among the pastry sheets and shape into a log. Brush edges of pastry with a little egg. Roll up to enclose the filling. Cut each roll in half or into small pieces and place, seam-side down, on the lined trays. Brush with a little more egg.
Bake for 25-30 mins or until the pastry is puffed and golden and the filling is cooked through. Set aside to cool slightly.
Serve sausage rolls with extra tomato sauce.