Bring a pot of salted water to a boil. Add the noodles and cook according to the package directions. Drain and toss with 2 tablespoons of the butter and 1 tablespoon of the parsley. Keep warm.
Meanwhile, melt the remaining 2 tablespoons butter over medium-high heat in an extra-large skillet. Add the beef, season with the paprika and some salt and pepper and cook until browned on all sides but still pink in the middle, 2 to 3 minutes. Remove from the skillet and set aside.
Add the mushrooms, onions and thyme to the skillet and season with salt and pepper. Cook until beginning to soften, 2 to 3 minutes. Add the hot stock and wine and cook for a minute until it reduces. Lower the heat and stir in the heavy cream and mustard. Add the beef back in, along with any juices on the plate. Cook for 1 minute so the beef is heated through. Turn off the heat and stir in the sour cream. Taste and adjust the seasoning.
Serve over the buttered noodles and garnish with the remaining parsley.