Place the sausage meat, cheese, sage and onion into a bowl and mix well.
Lay out the puff pastry on a floured surface then take the mixture and spread out evenly. Roll the pastry up like a swiss roll.
The cut into even slices. Place on a baking tray and cook in the oven for about 50 minutes or until golden brown. Remove from the oven and leave to cool on a wire rack. For best results leave until cold before eating.