In a bowl, marinate steak pieces in soy sauce.
Meanwhile in a microwaveable bowl, cook mushrooms on high until they have decreased in volume by half, about 4 to 5 minutes. Drain mushrooms and set aside. Discard liquid.
Combine water, dry mustard, sugar, and 1/2 teaspoon black pepper in a small bowl until a smooth paste forms; set aside.
Pat steak pieces dry. Heat oil in a 12 inch skillet over medium-high heat until just smoking. Place steak pieces in skillet and cook until browned on all sides, about 5 minutes. Transfer meat to large plate and set aside.
If necessary, add a bit more oil. Sauté mushrooms and onion until they begin to brown, scraping up browned bits on bottom of the pan, about 6 to 8 minutes.
Mix cornstarch and beef broth together in a small bowl.
Reduce heat to medium, add garlic, stir a minute or two, add tomato paste, 1/3 cup wine, mustard paste, broth and cornstarch mixture to skillet and continue cooking until sauce begins to thicken slightly.
Add steak back to pan and continue cooking until meat is cooked through and sauce is slightly thickened.
Season with salt, pepper and paprika. Remove from heat allow to cool just a couple of minutes. Stir in sour cream. Garnish with parsley
Serve over gluten free noodles, rice or mashed potatoes.