In a large skillet over medium-high heat, brown the ground beef with the chopped onions, garlic, and sliced mushrooms. Use a spoon to crumble the beef as it cooks.
Continue until the meat is no longer pink and the vegetables have softened, about 8-10 minutes.
Drain off any excess grease.
Reduce the heat to medium.
Stir in the softened cream cheese until it melts completely into the beef mixture.
Pour in the beef broth, heavy cream, water, and Worcestershire sauce.
Stir everything together until well combined and bring the sauce to a gentle simmer.
Let it cook for 5 minutes, allowing the flavors to meld and the sauce to thicken slightly.
Remove the skillet from the heat.
Season generously with salt and pepper to your liking. Gently stir in the sour cream until the sauce is smooth and uniform in color.
Serve immediately.
Stir the sour cream in *after* removing the skillet from the heat.
Adding it to a boiling sauce can cause it to curdle or separate.
