Bring a large pot of salted water to a boil. Cook the pasta until al dente according to the package directions.
Before draining, reserve approximately ⅔ cup (150 ml) of the pasta cooking water.
While the pasta cooks, melt the butter in a large skillet over low heat.
Add the heavy cream and warm gently for 2–3 minutes without bringing it to a rapid boil.
Gradually add half of the Parmesan, stirring until the cheese melts into the sauce.
Stir in 2 tablespoons of truffle paste and season with black pepper. Taste and add the remaining truffle paste and salt if needed.
Transfer the drained pasta to the skillet. Add ¼ cup of the reserved pasta water and toss until the sauce evenly coats the pasta.
If the sauce is too thick, add more pasta water, 1 tablespoon at a time.
Remove the skillet from the heat and stir in the remaining Parmesan. Add a few drops of truffle oil, if desired.
Serve immediately with additional Parmesan and freshly ground black pepper.