Very simply, just bring the spaghetti and salt to the boil, and simmer until the right consistency for your palate. My boy likes it soft, and other like it al dente, so choose your favoured options by the instructions on the packet you buy.
Drain the pasta, rinse with boiling water and drain again.
Return the pasta to a pan and add the carbonara sauce. Heat and stir until thoroughly hot.
Add butter, stir, then add milk until your carbonara reaches your desired consistency.
Serve with garlic bread.