Brown the beef and aromatics
In a 6‑quart (or similarly sized) soup pot over medium heat, add the ground beef, mushrooms (if using), chopped onion, and minced garlic. Cook for 5 to 7 minutes, breaking the meat up into small pieces, until the beef is no longer pink and the onion is softened.
Drain off excess fat from the pot if needed so your soup doesn’t get greasy.

Add liquid base and flavorings
Stir in the beef broth, optional bouillon paste (if using), and Worcestershire sauce. Increase heat to medium‑high and bring the mixture to a boil.

Cook the noodles
Once boiling, add the loosely crushed egg noodles. Reduce heat to medium and simmer, uncovered or partially covered (especially if cooking longer than 10 minutes), until the noodles are al dente per package instructions. Keep in mind they will continue softening when mixed with the creamy base.

Prepare the creamy thickening mixture
While the noodles cook, in a blender or using an immersion blender, combine the milk, sour cream, and flour. Blend until the mixture is silky smooth with no lumps.

Incorporate cream mixture and thicken
Slowly pour the blended cream mixture into the soup pot, stirring constantly to distribute evenly. Maintain medium heat and cook, stirring, until the soup comes to a simmer. Continue cooking for 3 to 4 more minutes until the soup thickens to your desired consistency.

Season and finish
Taste and adjust with salt and pepper. Be cautious: if you used bouillon paste, the soup may already have a fair amount of sodium.
Serve the soup hot, garnished with fresh chopped parsley in each bowl.

Serve and enjoy
The soup will thicken further as it cools; if needed, add a splash of stock or milk on reheating to loosen the texture.