Start by finely chopping the onion. Sweat this down in a frying pan with plenty of butter until soft and golden.
Slice the bacon rashers and add to the pan along with a small pinch of salt. Stir well and continue to fry. Once the bacon is cooked, remove from the heat and leave to one side.
Chop the spring onions and place into a mixing bowl.
Remove the rind from your cheese and grate it into the same bowl. Add the mustard and a pinch of both salt and pepper.
Once the bacon and onion mixture is completely cool, add this to the bowl along with 1 egg. Mix again until combined.
Crack and beat the other egg, ready to use as an egg wash.
Roll out the sheet of pastry and spoon the mixture onto it, leaving a gap all around the edges. Roll from the long side, sealing with final edge with egg wash.
Ideally, you should place the roll into the fridge for 1 hour to firm up before slicing, as this makes the swirls lovely and round and easier to handle.
Once sliced, egg wash the sides of each swirl. Place on a lined baking sheet and bake in the oven at about 190C for approx. 20 minutes until golden and crispy.
Leave to cool on a wire rack.