Heat oil In a large soup pot or Dutch oven over medium until the oil shimmers on the surface.

Lightly season the beef with salt and pepper. Add to the pot and let brown, stirring frequently to sear all sides of the strips (about 3 to 4 minutes). Transfer the beef to a bowl and set aside.

Deglaze the pot with the sherry/wine or a splash of broth, scraping up any stuck-on bits into the liquids.

Add the mushrooms, onion, and garlic to the pot; saute until the vegetables have softened, about 8 minutes.

Scootch the vegetables to the side and adding the tomato paste. Stir until fragrant.

Add a splash of the broth to the vegetables, and spoon the mustard and flour over them. Stir thoroughly - it might become a bit pasty; that's okay - for a minute or so to cook off the rawness of the flour.

Pour in the beef stock, Worcestershire sauce and bouillon (if using) and add the thyme. Increase the heat to medium-high and bring to a light bowl boil.

Add in the dried egg noodles. Reduce heat to maintain an active simmer and cook for 7-10 minutes (check the noodle's package for cooking time and make sure you cook them in the soup for at least that length).

In a medium mixing bowl combine the sour cream and heavy cream (if using). Whisk in a ladle of the hot soup until well combined. Pour the mixture into the soup and stir well.*

If using fresh thyme stems, fish them out now. The leaves should've dislodged from the stems into the soup.

Add the meat, along with any collected juices, back to the pot and simmer for a few more minutes to cook through.

Taste, and add more salt if needed.

Serve in individual bowls, topped with freshly chopped parsley.