How to Make It
In each of 2 large skillets, melt 1 tablespoon of the butter and 1/2 tablespoon of the olive oil over medium-high heat. Add the onions and mushrooms to each of the skillets and season both with salt and pepper. Cook until the onions have softened and the mushrooms are browned and tender, about 5 to 7 minutes. Add a ¼ cup of white wine to each skillet to deglaze the vegetables from the pan. Transfer to a slow cooker. Add the vegetable broth, sliced garlic, Worcestershire, and mustard to the pot and cook on high for 1 1/2 hours.
Bring a pot of salted water to a boil, cook the pasta until al dente and drain. Transfer the pasta to one large serving dish. Stir some butter into the noodles and top with the mushrooms and sauce. Swirl in the sour cream and season with salt and black pepper to taste. Garnish with chopped parsley and serve.