Step 1

In a large pot, bring 4 quarts water to a boil. Meanwhile, in a large bowl, using a silicone spatula, mash and stir the butter, miso, garlic, lemon juice, scallion whites and ¼ teaspoon pepper.

Step 2

To the boiling water, add the pasta and 1 tablespoon salt; cook, stirring occasionally, until al dente. Reserve about ½ cup of the pasta water, then drain. Immediately add the pasta to the butter-miso mixture, along with ¼ cup of the reserved pasta water. Toss vigorously, adding more pasta water, 1 tablespoon at a time, if needed, until lightly sauced; there should not be any liquid pooled in the bowl. Taste and season with salt and pepper. Serve sprinkled with the scallion greens and walnuts.

Step 3

Optional garnish: Finely grated Parmesan cheese OR furikake OR chili crisp