Cook spaghetti to al dente, according to package instructions. When cooked, reserve a cup of the pasta water and drain.
In a pan on medium heat, melt butter and stir occasionally. Once the butter begins to turn lightly brown and smells slightly nutty, lower heat and add the sliced shallot. Cook for another minute until softened. Remove from heat. Whisk in the miso, followed by a few splashes of the pasta water.
Toss in the spaghetti, parsley, parmesan, and salt and pepper if needed.