Crank the heat to high. Melt 2 tablespoons of the butter. Add the mushrooms and cook until all their liquid has been released and are nicely browned, 12 to 14 minutes. Add to the meatballs.
Lower the heat to medium and melt the remaining butter in the pan. Add the onion and cook until softened and translucent, 5 to 8 minutes. Sprinkle in the paprika.
Deglaze with the white wine and reduce by half, about 5 minutes. Scrape up the bits.
Stir in the stock, Dijon mustard, and the Worcestershire sauce.
Spoon the meatballs and mushrooms back into the skillet. Reduce the heat to low, cover the skillet, and simmer for 10 to 15 minutes, stirring occasionally to make sure the meatballs aren’t sticking.
Remove the skillet from the heat. Whisk a few spoonfuls of the hot broth into the sour cream. Stir the warm sour cream into the skillet until combined.
Adjust the seasoning to taste and scatter with the chopped parsley. Serve over buttered noodles.