Cook spaghetti in salted boiling water until al dente. Before draining, reserve 4 cups of pasta water. Drain and set aside.

In a large pan over medium heat, melt butter until sizzling. Add shiitake mushrooms—keep small ones whole, slice larger ones. Sauté until golden brown and slightly crispy.

Add garlic and sauté for 30 seconds until fragrant. Toss in the cooked pasta, mixing with the mushrooms.

Stir in miso and a cup of pasta water, letting it dissolve into the butter and coat the noodles.

Add parmesan, stir, then gradually add more pasta water and cheese, tossing until the sauce is creamy and coats the pasta.

Serve immediately with extra parmesan and cracked black pepper.