Lightly flour a work surface and roll out the sausagemeat to a 60cm/24in long sausage. Set aside. Flour the work surface again and quickly roll out the chilled pastry to a 15x60cm/6x24in rectangle.

Roll the filling into long sausage shape and place in the centre of the pastry. Make a small indentation along the top of the sausage and add a small amount of caramelised onion into the indentation.

If you buy ready-rolled pastry, just cut in half lengthways. Form half of the sausage meat filling into a long log shape, leaving about a finger width on each side of the pastry. Brush the sides ...