Bring a large pot of salted water to a boil. Add the penne pasta and cook according to package instructions until al dente, about 11 minutes. Reserve 1/4 cup of pasta cooking water and then drain the pasta.
While the pasta cooks, prepare the pesto. In a food processor, combine the fresh basil leaves, pine nuts, and garlic cloves. Pulse until finely chopped.
With the food processor running, slowly drizzle in the olive oil until the mixture is smooth and emulsified.
Add the grated Parmesan cheese, salt, and black pepper to the food processor. Pulse a few more times to combine. Set the pesto aside.
In a large skillet over medium heat, melt the unsalted butter. Pour in the heavy cream and bring to a gentle simmer, stirring frequently.
Add the prepared pesto to the cream sauce and stir to combine. If the sauce is too thick, add a little of the reserved pasta water to loosen it.
Add the drained pasta to the skillet and toss to coat the pasta evenly with the creamy pesto sauce.
Cook for an additional 1-2 minutes, stirring gently, until the pasta is heated through and the sauce clings to the pasta.
Serve immediately, garnished with extra grated Parmesan cheese if desired.