Bring a large pot of heavily salted water to a rolling boil. Add bucatini pasta and cook according to package instructions for about 8-10 minutes, or until al dente. Reserve 1 cup of pasta water, then drain the rest.

In a large sauté pan, melt 4 tablespoons of unsalted butter over medium heat. Stir in 2 tablespoons of white miso paste and coarsely ground black pepper. Cook for another 2 minutes.

Return the drained bucatini to the pot and pour the miso butter sauce over it, adding a splash of reserved pasta water. Stir vigorously for about 2 minutes.

Remove from heat and sprinkle with finely grated parmesan cheese. Serve immediately.