Melt 2 Tbsp of butter in the sauté pan and lightly brown the beef. There is no need to cook it completely, as it will be added in again, closer to the end. Remove and set aside.
Now add the rest of the butter to the sauté pan and sauté the onion until translucent, then add the mushrooms and cook until they reduce in size. Start a large pot of salted water for the noodles. Bring to a boil and add the noodles.
Add the wine, deglaze the pan and continue cooking until the wine has mostly evaporated. Now add back the meat and residual juices and the nutmeg and cook for another few minutes. Don’t overcook, you want the meat to be slightly pink.
Drain the noodles after they have cooked slightly under the recommended time and add the sour cream into the hot noodles immediately and then add the meat mixture. Stir well until the mixture is well mixed and serve on warm plates. You may garnish with freshly chopped parsley if desired.