Add the pasta to boiling salted water.
Half way through the pasta cooking time, in a sauce pan add the ricotta and warm it up at low-medium flame. Add 1/2 cup of pasta water to the ricotta and mix well to obtain a smooth sauce.
Once the pasta is al dente, drain it and add it to the ricotta sauce. Turn off the flame and mix well.
Add as much grated parmigiano cheese as you like, mix again and serve immediately.