Bring a large pot of salted water to a boil. Add the fettuccine and cook according to package instructions until al dente. Reserve 1 cup of pasta water, then drain the pasta.

In a skillet over medium heat, melt the butter. Continue cooking, stirring frequently, until the butter turns golden brown and has a nutty aroma, about 5-7 minutes.

Add the sliced mushrooms and minced garlic to the brown butter. Sauté until the mushrooms are browned and tender, about 5-7 minutes.

Add the cooked pasta to the skillet with the mushrooms. Toss to combine, adding reserved pasta water as needed to create a sauce. Stir in parmesan cheese, thyme, salt, and pepper.

Plate the pasta and garnish with chopped parsley and additional parmesan cheese. Serve immediately.