Add to the pot the mushrooms, onion, and garlic; saute until the vegetables have softened, about 3 minutes.
Stir in the tomato paste and Worcestershire sauce.
Pour in the beef stock and bring to a boil.
Add in the noodles. Reduce heat to a simmer and cook for 5-7 minutes until al dente.
In a bowl or large measuring cup, combine the sour cream and flour. Whisk in 1 cup of the hot soup; pour mixture back into the pot. Cook and stir for 1-2 minutes to thicken.
Add cooked meat back to the pot and heat through. Taste, and adjust seasoning with a little more salt and pepper, if necessary.