Bring a large pot of water to the boil. When it has reached a rolling boil add a large pinch of salt and cook pasta according to packet instructions, removing 1 minute before the instructions suggest. Make sure it is still al dente as it will cook a little more in the oven. Drizzle with a little olive oil to stop it sticking together and leave it in the colander until the sauce is ready.
Place a frying pan over medium heat, place the bacon rind in (this will provide the oil to cook the onion). When the fat has seeped out of the bacon rind remove and discard.
Add a little olive oil if necessary then add the onion and bacon.
When the onion is soft and the bacon is cooked add the chicken stock and allow to reduce for 5 minutes on a high heat.
Take the mixture off the heat and stir through the parmesan and the mozzarella, allowing it to melt into the sauce.
Add the pasta to the mixture and stir to combine.
Pour the pasta into a casserole dish, cover with breadcrumbs and bake for 30 minutes, or until the top is golden and crunchy.