Heat the oil in a pan and add the onion. Cook until soft the add the mushrooms and garlic. Raise the temperature slightly and cook for around 5 minutes. Add the pine nuts and pesto for another 2 minutes.
Whisk the cream cheese and milk together, then pour into the pan, mix it well in and simmer gently 2 to 3 minutes until hot keep stirring now and again.
Meanwhile boil some salted water and boil the pasta and cook to the instructions on the packet. Drain and serve between four bowls.
Add the basil and a little salt and pepper to the sauce and toss through, then add the sauce to your pasta.