01 - Rinse rice under cold water. In a saucepan, combine rice, water, and salt. Bring to a boil, cover, reduce heat and simmer for 15 minutes until water is absorbed. Remove from heat and let stand, covered, for 5 minutes. Fluff with a fork.
02 - Toss beef strips with salt, black pepper, and flour until evenly coated.
03 - Heat 1 tbsp butter and olive oil in a large skillet over medium-high heat. Add beef in batches and sear until browned but not cooked through, about 1 to 2 minutes per side. Remove and set aside.
04 - Add remaining 1 tbsp butter to the skillet. Cook onions for 3 minutes until softened. Add garlic and mushrooms; sauté for 5 to 7 minutes until mushrooms are golden and moisture has evaporated.
05 - Stir in tomato paste and cook for 1 minute. Pour in beef broth, scraping browned bits from pan.
06 - Reduce heat to low. Stir in sour cream, Dijon mustard, and Worcestershire sauce until smooth.
07 - Return beef and juices to skillet. Simmer gently for 3 to 5 minutes until beef is tender and sauce thickens slightly. Avoid boiling.
08 - Adjust seasoning to taste. Serve hot beef mixture over rice and garnish with chopped parsley.