Bring a pot of water to a hard boil, and add the pasta and salt as per instructions on the package.
Boil on med-high flame for 7-9 minutes, until 'Al Dante', firm but not hard.
Rinse with cold water to stop the cooking process, and strain. Set aside and add some oil so it doesn't stick in clumps.
Melt butter on a medium flame, add garlic and mushrooms until soft and golden.
Add heavy cream and bring it to a boil. Sift some cornstarch into the grated parmesan cheese, and while adding to the cream, squeeze some lemon juice into the mixture at the same time (this will make it smoother, and not make the mixture clumpy.)
Fork the pasta into...