01 - Rinse the basmati rice under cold water until the water runs clear. In a saucepan, bring 2 cups of water to a boil. Add the rice, salt, and butter. Reduce heat to low, cover, and simmer for 12 to 15 minutes until tender and water is absorbed. Fluff with a fork and keep warm.
02 - Toss the beef strips with flour, salt, and freshly ground black pepper until evenly coated.
03 - Heat 1 tablespoon olive oil and 1 tablespoon butter in a large skillet over medium-high heat. Sear half of the beef strips until browned but still pink inside, about 1 to 2 minutes per side. Remove to a plate. Repeat with the remaining beef, adding more oil if needed.
04 - In the same skillet, add the remaining butter. Sauté the sliced onions until soft and translucent, about 4 minutes. Add minced garlic and sliced mushrooms; cook until mushrooms are browned and moisture evaporates, approximately 5 to 6 minutes.
05 - Stir in tomato paste, Dijon mustard, and paprika. Cook for 1 minute to develop flavors.
06 - Pour in beef broth, scraping any browned bits from the pan. Simmer gently for 3 minutes to reduce slightly.
07 - Lower the heat. Stir in sour cream until fully incorporated without boiling. Return the beef along with any accumulated juices to the skillet. Simmer gently for 2 to 3 minutes until beef is cooked through and the sauce is creamy. Adjust seasoning with salt and pepper to taste.
08 - Plate the beef mixture over the prepared basmati rice and garnish with chopped fresh parsley.