Make the sauce
Bring a large pot of water to a boil. In a large frying pan over medium-high heat, melt the butter. Add the shallot and sauté until lightly golden, 2–3 minutes. Add the mushrooms and cook, stirring, until they have softened and released most of their liquid, about 5 minutes. Add the flour and stir to incorporate. Stir in the wine and the broth and cook until the wine evaporates slightly, about 2 minutes. Remove from the heat and stir in the sour cream and the 2 tablespoons parsley. Season with salt and pepper.