Season the beef strips with the salt, black pepper, and smoked paprika. Heat the olive oil and 1 tablespoon of butter in a large skillet over high heat. Sear the beef in a single layer, without moving, for about 1 to 2 minutes per side until browned. Work in batches to avoid overcrowding. Transfer the beef to a plate.
Reduce heat to medium. Add the remaining 2 tablespoons of butter to the same skillet. Add the sliced mushrooms and diced onion, and cook for 5 to 6 minutes, stirring occasionally, until the mushrooms are golden and the onion is softened.
Add the garlic and cook for 30 seconds until fragrant. Sprinkle the gluten free flour blend over the vegetables and stir for about 1 minute to coat everything evenly.
Slowly pour in the beef broth while stirring constantly. Add the tamari and dijon mustard. Bring the sauce to a simmer and cook for 3 to 4 minutes until it thickens.
While the sauce simmers, cook the gluten free egg noodles according to the package directions. Drain and set aside.
Remove the skillet from the heat and stir in the sour cream until smooth and creamy. Return the seared beef and any accumulated juices to the skillet and stir gently to combine.
Serve the stroganoff over the cooked gluten free egg noodles and garnish with fresh chopped parsley.