Bring a large pot of salted water to a boil. Add 8 ounces of penne pasta and cook according to package instructions until al dente. Drain and set aside, reserving a little pasta water for later if needed.
Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Add the thinly sliced beef sirloin in a single layer without overcrowding. Sear for 2-3 minutes on each side until browned but not fully cooked through. Remove from the pan and set aside.
In the same skillet, add the diced onion and cook for 3-4 minutes until translucent. Add minced garlic and sliced mushrooms, sautéing until mushrooms are golden and tender, about 5-7 minutes.
Pour 1 cup of beef broth into the skillet, scraping up any browned bits from the bottom. Stir in 1 tablespoon Worcestershire sauce and bring to a simmer.
Lower the heat and stir in 1 cup of sour cream until the sauce is smooth and creamy. Return the beef to the skillet and cook for another 2-3 minutes until the beef is heated through and the sauce thickens slightly. Season with salt and pepper to taste.
Add the cooked penne pasta to the skillet, gently tossing to coat every piece in the rich sauce. If the sauce seems too thick, add a splash of reserved pasta water to loosen it. Garnish with chopped fresh parsley for a pop of color and freshness. Serve immediately and enjoy.