Bring a large pot of salted water to a boil and cook the long thin pasta according to package directions for al dente, about 8-10 minutes.

In a small bowl, whisk together the reserved pasta water and white miso paste until smooth.

Melt cubed butter in a skillet over medium heat, then add coarsely ground pepper and stir for a minute.

Pour the miso mixture into the skillet, stir gently, and then add the cooked pasta, remaining butter, and Parmesan cheese.

Toss continuously until the cheese melts and sauce coats the pasta. Adjust consistency with reserved pasta water if needed.

Plate the pasta and garnish with green onions or chili crisp before serving.