Cook the noodles:

Prepare the egg noodles by boiling them in a large pot of well-salted water, following the instructions on the package until al dente. Drain the noodles once they are cooked. For optimal timing, add the noodles to the boiling water when beginning Step 4.

Sauté the steak:

As the pasta water heats up, melt 2 tablespoons of butter in a large sauté pan over medium-high heat. Season the steak with salt and pepper, then add it to the pan in a single layer. Allow the steak to sear undisturbed for approximately 3 minutes, then flip and cook for another 2-3 minutes until browned on both sides. Remove the steak from the pan and set it aside on a clean plate. If your pan cannot fit all the steak at once, cook it in two batches, using 1 tablespoon of butter for each.

Sauté the vegetables:

To the same pan, add the remaining 2 tablespoons of butter and let it melt. Add the sliced onions, cooking for about 3 minutes until softened. Next, add the mushrooms and sauté for another 5-7 minutes, stirring occasionally, until the mushrooms release their moisture and begin to brown. Stir in the garlic and cook for 1 minute, then pour in the white wine to deglaze the pan. Use a spoon to scrape up any brown bits from the bottom of the pan, then allow the wine to cook down for about 3 minutes.

Prepare the sauce:

In a separate bowl, whisk together the beef stock, Worcestershire sauce, and flour until smooth. Pour this mixture into the sauté pan and stir to combine. Let the sauce simmer for 5 minutes, stirring occasionally. Once the sauce has thickened, stir in the Greek yogurt (or sour cream) and the cooked steak, mixing everything together. Taste and adjust seasoning with more salt and pepper, if needed.