Bring a large pot of salted water to a rolling boil. Add pasta and cook until al dente (about 1 minute less than package directions). Reserve 1 cup of pasta water before draining.

While pasta cooks, heat olive oil in a 12-inch skillet over medium-high heat. Add mushrooms in a single layer (work in batches if needed). Cook undisturbed for 4 minutes until golden brown on one side. Stir and cook another 3-4 minutes until deeply browned and any liquid has evaporated.

Reduce heat to medium. Add garlic and cook 30 seconds until fragrant. Pour in wine (or broth) and scrape up any browned bits from the pan. Let simmer 2 minutes until reduced by half.

Add 1/2 cup reserved pasta water and bring to a gentle simmer. Toss in drained pasta and stir well to coat. Remove from heat.

Add Parmesan and butter. Toss vigorously until the sauce turns creamy and clings to the pasta. If too thick, add more pasta water 1 tablespoon at a time. Season with salt and pepper.

Serve immediately, topped with parsley if desired. The sauce will thicken as it cools.