Bring a large pot of salted water to a boil. Cook the pappardelle according to the package directions until al dente. Reserve 1 cup of the pasta water before draining.

Meanwhile, heat the olive oil and 2 tablespoons of the butter in a large skillet over medium-high heat.

Add the mushrooms and cook for 8-10 minutes, stirring occasionally, until they release their moisture and become deeply golden brown. Don't rush this step—the browned mushrooms add most of the flavor to the dish.

Reduce the heat to medium and stir in the remaining 2 tablespoons of butter and the garlic. Cook for 30 seconds, stirring constantly, until fragrant.

Add the cooked pappardelle to the skillet along with 1/4 cup of the reserved pasta water. Toss until the pasta is coated in the garlic butter sauce.

Remove the skillet from the heat and stir in the Parmesan cheese and parsley. Continue tossing until the cheese melts into a silky sauce. Add more pasta water as needed to loosen the sauce.

Season with salt and black pepper to taste.

Serve immediately with extra Parmesan cheese and parsley sprinkled over the top.