Cook the pasta in a large pan of boiling water as directed on the packet. Skin the sausages and roll the sausage meat into bite size balls. Fry in a little oil until browned all over and cooked through. Remove the meatballs from the pan.
Add the onion and garlic to the frying pan and cook gently for several minutes to soften the onions. Add the Philly to the onions with the stock (or a little water) and mustard. Gently heat until the Philly has melted, then stir in the parsley and meatballs.
Meanwhile drain the pasta and divide between 4 pasta bowls. Top with the meat balls and spoon over the Philly sauce to serve.