01 - Rinse rice under cold water until clear. Combine rice, water, salt, and butter in a saucepan. Bring to a boil over medium-high heat, reduce to low, cover, and simmer for 15–18 minutes until water is absorbed and rice is tender. Remove from heat, let stand covered for 5 minutes, then fluff with a fork.
02 - Toss beef strips with flour, salt, and pepper. Heat 1 tbsp olive oil in a large skillet over medium-high heat. Sear half the beef for 1–2 minutes until browned; transfer to a plate. Repeat with remaining oil and beef.
03 - In the same skillet, melt butter. Cook onion for 2 minutes until softened, add garlic and cook 30 seconds. Add mushrooms and cook 5–6 minutes until browned and liquid evaporates.
04 - Stir in tomato paste and mustard. Pour in beef broth, scraping browned bits from the skillet. Simmer for 5 minutes.
05 - Lower heat to medium-low. Stir in sour cream and smoked paprika, return beef and juices to skillet. Warm gently for 2–3 minutes until beef is cooked through and sauce is creamy; do not boil. Adjust seasoning; sprinkle with parsley.
06 - Spoon rice onto plates and top with beef mixture. Garnish with extra parsley if desired.