01 -
Heat olive oil in a skillet over medium heat. Add sliced onions and a generous pinch of salt. Cook slowly, stirring occasionally, until onions are deeply golden, approximately 15–20 minutes. Allow to cool.
02 -
In a mixing bowl, combine ground sausage, caramelised onions, thyme, salt, and pepper. Add Gruyère cheese and Dijon mustard if using. Mix until fully incorporated.
03 -
Preheat the oven to 200°C. Line a baking sheet with parchment paper.
04 -
On a lightly floured surface, unroll puff pastry sheets and cut into rectangles approximately 10×15 cm. Place a portion of sausage filling along one long edge of each rectangle, fold pastry over, and seal the edges firmly with a fork. Place seam-side down on the prepared tray.
05 -
Brush the tops of the pastry with beaten egg for a glossy finish.
06 -
Bake in the centre of the oven for 20–25 minutes, or until the pastry is deeply golden and crisp. Allow rolls to cool slightly on a rack before serving.