Heat the olive oil in a large skillet over medium-high heat. Add the beef strips and cook for 3-4 minutes, or until browned on all sides. Remove the beef from the skillet and set aside.
Add the butter to the same skillet and melt it over medium heat. Add the chopped onion and sliced mushrooms and cook until they are soft and tender, about 5 minutes.
Add the minced garlic to the skillet and cook for 1 minute, or until fragrant.
Pour in the beef broth and stir to combine. Add the beef strips back to the skillet and simmer for 5 minutes, or until the beef is cooked through.
Remove the skillet from the heat and stir in the sour cream and heavy cream. Season with salt and pepper, to taste.
Garnish with chopped fresh parsley and serve hot.
This dish is delicious on its own or served over cauliflower rice or zucchini noodles to keep it keto-friendly. Enjoy!