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