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 1/2 cup of pasta water, then drain the pasta and set aside.
While the pasta cooks, prepare the pesto. In a food processor, combine the basil leaves, 1/4 cup grated Parmesan cheese, pine nuts, and garlic cloves. Pulse until finely chopped.
With the food processor running, slowly stream in the olive oil until the mixture is smooth and emulsified. Season with 1/2 teaspoon salt and 1/4 teaspoon black pepper. Set the pesto aside.
In a large skillet over medium heat, melt the butter. Add the heavy cream and bring to a gentle simmer, stirring frequently.
Stir in 1/4 cup grated Parmesan cheese until melted and the sauce is smooth.
Add the prepared pesto to the cream sauce and stir to combine. If the sauce is too thick, add reserved pasta water a little at a time until desired consistency is reached.
Add the cooked pasta to the skillet and toss gently to coat the pasta evenly with the creamy pesto sauce.
Cook for an additional 1-2 minutes to heat through. Taste and adjust seasoning with salt if needed.
Serve immediately, garnished with extra Parmesan cheese if desired.