Sear the Beef:
In a large pot or Dutch oven over medium-high heat, add olive oil. Sear the beef slices for 2-3 minutes until browned. Remove and set aside.

Cook the Vegetables:
Add the diced onion and cook for 2 minutes until softened. Stir in garlic and mushrooms, cooking for another 3-4 minutes until fragrant.

Simmer the Soup:
Pour in beef broth and water. Stir in Worcestershire sauce, Dijon mustard, smoked paprika, salt, and black pepper. Return the beef to the pot. Bring to a boil, then reduce heat and let simmer for 15 minutes.

Cook the Noodles:
Add the egg noodles and cook for 8-10 minutes until tender.

Make it Creamy:
Reduce heat to low. Stir in sour cream and heavy cream (if using) until fully combined. Do not let the soup boil.

Serve:
Ladle into bowls, garnish with fresh parsley, and serve warm.