Wash and dry all produce. Bring a medium pot of salted water to a boil. Trim, then thinly slice scallions, separating greens and whites. Cut mushrooms into thin slices (about ¼ inch thick).

Heat 1 TBSP olive oil in a large pan over medium-high heat. Add mushrooms and season with salt and pepper. Cook, tossing occasionally, until browned and a little crisp, 5-7 minutes. Remove from pan and transfer to a paper-towel-lined plate. Rinse out pan and wipe dry.

Once water boils, add fusilli to pot. Cook, stirring occasionally, until al dente, 9-11 minutes. Scoop out 1 cup pasta cooking water, then drain.

Lower heat under pan used for mushrooms to medium and add 2 TBSP plain butter. Once melted, add scallion whites and cook until just softened, 1-2 minutes. Add flour and stir to combine. Cook, stirring often, until flour loses its raw smell, about 2 minutes. Whisk in milk and ⅓ cup pasta cooking water, making sure to eliminate any flour clumps. Let simmer until slightly thickened, 3-4 minutes.

Add cream cheese to pan and stir to melt, then stir in mushrooms and fusilli. Stir garlic herb butter into pan. Season with salt and pepper. TIP: Everything should be coated in a loose, creamy sauce. If very thick, add more pasta cooking water 1 TBSP at a time.

Divide pasta between plates and sprinkle with Parmesan. Garnish with scallion greens and serve.