Preheat a skillet to medium-high heat with the olive oil. Add the mushrooms, and cook for 7-10 minutes until browned and wilted. Add the onion and garlic and a sprinkle of salt. Cook for 3 minutes more until onion begins to soften, stirring so the garlic doesn't burn.

When the veggies are all soft, sprinkle the flour over the mixture and stir to coat evenly. Let the flour cook for 90 seconds or so (turn down the heat if the veggies start to brown too much), and pour in the beef broth. Stir to create a thin gravy, then add the sour cream and Worcestershire sauce.

Let the sauce simmer for 5 minutes before serving. If the gravy becomes too thick, add water 2 tablespoons at a time to thin. If the gravy is thin, let simmer for a few minutes more to thicken before serving. Taste, and add salt if needed.

To serve, toss all the pasta with the gravy, OR serve gravy over pasta with an extra dollop of sour cream on top, if desired.