Place the sausage meat in a bowl with the onion, herbs, mustard if using, and a little salt and pepper. Mix until evenly combined.

Unroll the puff pastry and cut it in half lengthways to make two long strips.

Divide the sausage mixture into two equal portions and shape each into a long sausage down the centre of each pastry strip.

Brush one edge of each pastry strip with beaten egg, then fold the pastry over the filling and press the edges together to seal.

Cut each long roll into 4 pieces. Score the tops lightly with a knife, then brush with beaten egg and sprinkle with seeds if using.

Lightly spray the air fryer basket with oil, then place the sausage rolls in the basket, leaving space between each one. Cook in batches if needed.

Air fry at 180°C for 12–15 minutes, turning halfway through if needed, until the pastry is golden and crisp and the sausage meat is cooked through.

If using a food thermometer, the centre should reach 75°C before serving.