Cook pasta as per package instructions until al dente. Reserve ½ cup pasta water, then drain.
Heat butter in a medium pot over medium-high heat. Sauté diced onion for 5 minutes until golden.
Add garlic and mushrooms, cooking for another 5 minutes until mushrooms soften.
Stir in flour, cook for 1 minute. Add wine and broth, bringing to a boil. Reduce heat and simmer for 5 minutes until sauce thickens.
Stir in vegan sour cream, parsley, salt, and pepper.
Combine pasta with sauce, tossing well. Add reserved pasta water if needed for desired consistency.
Serve with extra parsley on top.