Preheat the oven to 180 degrees Celsius.
Start by rolling out your puff pastry to 2-3 mm thick. You want it to be shaped as a long rectangle, with the longest side on the horizontal. Then cut the pastry in half on the horizontal, so that you have two long rectangular pieces of pastry. Leave to one side.
Get a large baking tray and line with baking parchment.
Cut the smoked cheese into 12 small chunks.
Get a large bowl and squeeze the sausage meat out of the skins into the bowl. Discard the skins. Use your (clean) hands to squish the sausage meat together, then form it into 12 balls.
Push the cheese into the centre of each sausage ball and make sure that the sausage meat is full enveloping each one.
Lay the sausage balls evenly onto the puff pastry, six on each piece. Fold each piece of pastry over on the horizontal so that you have two long sausage rolls, covering the sausage meat in the middle. Use a knife to cut the pastry between each sausage ball to form 12 sausage rolls.
Use a fork to crimp the pastry around each sausage roll, making sure the sausage meat is fully covered by the pastry. Use a knife to poke a small hole in the top of each one.
Crack the egg into a small bowl and beat. Brush the top of the sausage rolls with the beaten egg and sprinkle over the poppy seeds. Put in the oven and bake for 25 minutes until risen and golden.