Season the cubed beef generously with salt and pepper. Heat olive oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Brown the beef in batches, ensuring not to overcrowd the pan. Remove the browned beef and set aside.

Reduce the heat to medium. Add the diced onion to the pot and sauté for 5-7 minutes until softened and translucent. Add the sliced mushrooms and cook until they have released their moisture and started to brown, about 8-10 minutes.

Stir in the minced garlic and dried thyme, cooking for 1 minute until fragrant. Sprinkle the flour over the vegetables and stir continuously for 2 minutes to cook out the raw flour taste, creating a roux.

Slowly whisk in the beef broth and water, scraping up any browned bits from the bottom of the pot. Return the browned beef to the pot. Bring the mixture to a boil, then reduce heat to low, cover, and simmer for 35-40 minutes, or until the beef is fork-tender.

Stir in the Worcestershire sauce and heavy cream. Heat gently for 5 minutes, ensuring the soup does not boil after adding the cream. Taste and adjust seasoning with additional salt and pepper as needed.

Ladle the creamy mushroom soup into bowls. Garnish generously with fresh chopped parsley before serving hot.