In a large stock pot, add water.
Bring the water to a boil.
Add the salt and spaghetti.
Cook according to the package instructions.
In a large skillet, add butter and onion.
Cook for 1 minute, or until onion is translucent.
Add cream cheese and break it up with your spatula.
Cook for 3-4 minutes, or until the cream cheese "melts."
Add the sour cream and salt.
Cook for 1 minute.
Taste for salt. Adjust if needed.
Add cooked spaghetti to the skillet.
Immediately turn off the heat.
Toss the spaghetti in the cream sauce. Coat well.
Serve. Top with parsley and parmesan cheese, if using.