Preheat your oven to 200°C (390°F) and line a baking sheet with parchment paper.
Finely chop the onion and sauté in a skillet over medium heat until soft and fragrant, about 5 minutes. Let it cool slightly.
Remove the sausage from its casings if necessary, then place it in a large mixing bowl. Add the cooled onion, minced garlic, herbs, breadcrumbs, salt, and pepper.
Mix everything together thoroughly until well combined, ensuring the seasoning is evenly distributed throughout the sausage.
Gently roll out the puff pastry sheets on a floured surface to about 0.5 cm thickness. Cut each sheet into rectangles approximately 10x15 cm.
Divide the sausage mixture into equal portions and shape each into a log about 12 cm long. Place each sausage log along one edge of the pastry rectangle.
Fold the pastry over the sausage, sealing the edges with a little water if needed, and pinch to close securely. Place seam-side down on the prepared baking sheet.
Brush the tops of each roll with the beaten egg for a shiny, golden finish. Lightly score the tops with a knife to allow steam to escape during baking.
Bake in the preheated oven for 25-30 minutes, or until the pastry is deeply golden and crisp, and the filling is bubbling.
Remove from the oven and let rest for 5 minutes. The crust will crackle and the aroma will be irresistible.
Slice if desired and serve warm or at room temperature, enjoying the crispy exterior and juicy filling in every bite.
