Step 1

Prep veggies: Rinse 8 oz mushrooms in cold water (no need to pat them dry—see note 1). Slice mushrooms. Thinly slice the white and light green parts of 2 scallions (for cooking). Then, mince the dark green part of the scallions and set aside (for finishing).

Step 2

Cook pasta: Bring a large pot of salted water to a boil. Add 6 oz dried bucatini and cook until al dente according to package directions. Scoop out 1 cup of the pasta water and set aside, then drain noodles.

Step 3

Meanwhile, sear mushrooms: Heat a large dry skillet over medium-high heat. (It's hot enough when you flick water on the pan and large droplets bounce and skid around). Scatter mushrooms in skillet. Cook, stirring infrequently, until water has evaporated and mushrooms are brown on both sides, 5 to 8 minutes (see note 1). Reduce heat to low, and continue cooking mushrooms for about 1 minute while the skillet cools slightly.

Step 4

Build sauce: Push mushrooms to the edges of the skillet. In the middle of the skillet, add 3 tablespoons butter, 2 cloves minced garlic, and the white/light green parts of the scallion. Cook until fragrant, about 1 minute. Then stir to coat mushrooms in butter. Cook, stirring frequently, until garlic is pale golden (avoid burning), 2 to 3 minutes. Add 2 tablespoons white miso , 2 teaspoons sriracha, and ⅔ cup of the reserved pasta water to the skillet. (Save remaining pasta water for finishing step). Whisk until the miso evenly mixed into a smooth sauce.

Step 5

Finish: Add cooked pasta to the skillet, toss until well coated. Scatter in ¼ cup finely grated Parmesan cheese and the minced dark green part of the scallions. Toss again, adding splashes of extra pasta water if/as needed, until the noodles are coated in a silky sauce. Finish with Black pepper and more Parmesan cheese, to taste.