Preheat the oven to 200ºC, fan 180ºC, gas 6. Heat the oil in a small pan and add the onion. Cook until soft, then add the carrot and apple. Transfer to a bowl, then mix in the sage and pork mince until well combined.
Unroll the pack of ready-rolled puff pastry, then cut in half lengthways. Divide the mixture in two, and place in the middle of each strip of pastry. Brush all edges of the pastry with the beaten egg, reserving some for the top. Fold the pastry over the filling, and seal by pressing gently on each roll.
Flip the roll so the seal is on the underside of each roll. Cut each strip into 8 rolls. Brush the tops with the remaining beaten egg, then sprinkle with the poppy and sesame seeds. Place the rolls on a baking tray and bake for 25-30 minutes until crisp and golden, and the pork is cooked through.
Cook's tip: make one giant sausage roll by doubling the sausage filling in the above recipe. Place the filling in the centre of a piece of ready-rolled puff pastry. Brush the pastry with the beaten egg, then roll the pastry over the filling. Flip and lay seam-side down on a baking tray. Cut diagonal slits across the top, brush with a little more of the beaten egg and sprinkle with sesame and poppy seeds. Bake for 55 mins, then leave to cool before slicing up and serving.
Or, use ready-made sausage meat for your filling and season with dried herbs. Make the sausage rolls as usual, then brush the tops with milk rather than egg. Top with freshly ground black pepper.